S13C-1808
Reasoning Under Uncertainty in Seismic Hazard Analysis: Modeling the Joint Probability of Earthquake, Site and Ground-Motion Parameters Using Bayesian Networks
Empirical ground-motion models for use in seismic hazard analysis are commonly described by regression models, where the ground-motion parameter is assumed to be dependent on some earthquake- and site- specific parameters such as magnitude, distance or local vs30. In regression analysis only the target is treated as a random variable, while the predictors are not; they are implicitly assumed to be complete and error-free, which is not the case for magnitudes or distances in earthquake catalogs. However, in research areas such as machine learning or artificial intelligence techniques to overcome these issues exist. Borrowing from these fields, we present a novel multivariate approach to ground-motion estimation by means of the Bayesian network (BN) formalism. This elegant and intuitively appealing framework allows for reasoning under uncertainty by modeling directly the joint probability distribution of all variables, while at the same time offering explicit insight into the probabilistic relationships between variables. The formalism provides us with efficient methods for computing any marginal or conditional distribution of any subset of variables. In particular, if some earthquake- or site-related parameters are unknown, the distribution of the ground motion parameter of interest can still be calculated. In this case, the associated uncertainty is incorporated in the model framework. Here, we explore the use of BNs in the development of ground-motion models. Therefore, we construct BNs for both a synthetic and the NGA dataset, the most comprehensive strong ground motion dataset currently available. The analysis shows that BNs are able to capture the probabilistic dependencies between the different variables of interest. Comparison of the learned BN with the NGA model of Boore and Atkinson (2008) shows a reasonable agreement in distance and magnitude ranges with good data coverage.
S13C-1809
Model Selection in Seismic Hazard Analysis: an Information-Theoretic Perspective
Although the methodological framework of probabilistic seismic hazard analysis (PSHA) is well established, the selection of models to characterize seismic source properties and of models to predict the ground motion at the site(s) of interest remains a major challenge. Information theory provides a powerful theoretical framework which can guide this selection process in a consistent way. From an information-theoretic perspective, the appropriateness of models can be expressed in terms of their relative entropy and hence in physically meaningful units (bits). In contrast to hypothesis testing, which requires ad-hoc decisions regarding significance levels, as well as in contrast to Bayesian inference, which for the assignment of prior probabilities requires models to be mutually exclusive and collectively exhaustive, information-theoretic model selection does not depend on such ad-hoc assumptions. The key ingredient , the Kullback-Leibler divergence, is easily estimated from the statistical expectation of log-likelihoods of observations for the models under consideration. In the present study, data-driven ground-motion model selection ibased on Kullback-Leibler divergence differences is illustrated for a set of simulated observations of response spectra and macroseismic intensities. The application of this approach to real data using the model generating data set for the Abrahamson and Silva (1997) ground-motion model demonstrates the superiority of the information-theoretic perspective in comparizon to earlier attempts on data-driven model selection (e.g. Scherbaum et al. 2004). In a companion poster (Delavaud et al, 2008) we systematically apply this method to observations from California.
S13C-1810
Ground Motion Model Selection Based on Macroseismic Intensities: Application to Californian Earthquakes
Considering the increasing number of ground motion prediction equations (GMPE) available for seismic hazard assessment, there is a huge need for an efficient and robust method to select and rank these models. Although information contained in macroseismic intensities is not yet perfectly understood, we believe that this under-exploited large amount of data can be successfully used for model selection. We apply criteria based on information theory to rank GMPE for Californian type earthquakes from both pseudo-spectral accelerations (PSA) and macroseismic intensities (MI) data. Synthetics are computed for 10 Californian earthquakes by 22 different GMPE for PSA and combined with the equation by Atkinson and Sonley (2000) for MI. In order to reduce uncertainty, we take into account the fault geometry to directly compute the intrinsic distance metric of each prediction equation. Site effects and inter-event variability are also incorporated. Rankings based on PSA and MI data are found to be consistent, and we explore the relative information of intensity versus response spectral data. We test the robustness of this information-theoretic method, which is presented in a companion paper (Scherbaum et al., 2008) in more details, and also perform a sensitivity study, in terms of sampling and extended source parameters.
S13C-1811
Modeling of seismic process and Coulomb stress transfer in the area of Murindó- Colombia, and implications for seismic hazard
For this study, we used shallow earthquakes located in the area of Murindó - Colombia (latitudes between 6º to 8º and longitudes between -75.5° to -78.0°) with magnitudes ML between 0.7 and 6.1. The catalog of earthquakes, compiled by Red Sismológica Nacional de Colombia between 1993 and 2007, has magnitude of completeness MC = 2.7, and b- value between 0.6 and 2.0. We relocated earthquakes using a Double Difference method and the results suggest that a portion of the seismicity occurs under the Atrato River valley and confirm the results of relocations obtained with JHD in previous studies. To calculate Coulomb stress changes transferred during a seismic sequence on October 17-18, 1992, we modeled the sequence using two left-lateral near-vertical faults with an uniform slip of 0.6 m and 1.3 m, oriented SSW- NNE and consistent with computed focal mechanisms and magnitudes. The results are consistent with a precursory faulting on October 17 that facilitated the rupturing during the main earthquake on October 18, 1992. Stress changes transferred to other areas are in the range from -5 to 5 bars (-0.5 to 0.5 MPa). We conclude that the b-values are relatively low to the north and relatively high to the south, the latter reflecting conditions of relaxed stresses of the crust during 1993-2007. Additionally, relocations of the earthquakes suggest that the seismicity may be ocurring on a fault that has not been mapped with an orientation similar to other mapped faults nearby. We conclude that the 1992 Murindó seismic sequence was a case in which a large earthquake was facilitated by a smaller foreshock and most of the aftershocks and the microseismicity are explained by our model of Coulomb stress changes and hence our results have implications on the seismic hazard in Colombia.
S13C-1812
The Development of Earthquake Intensity Attenuation Model in Northern-China and Its Application in Quantitatively Estimating the Earthquake Location and Magnitude
A systematic strategy has been proposed by Bakun and Wentworth in 1997 for bounding the earthquake epicentral region and magnitude from historical intensity data only. This technique is quantitative and particularly appropriate for historical earthquakes which have few intensity data or occurred near offshore. With this technique developed by Bakun and Wentworth, we have focused our study region in Northern- China in which there have been a lot of moderate or large historical and modern earthquakes occurred since last a few centuries. First, ten earthquakes with modern instrumental records with magnitude ranging from Ms 5.3 to 7.8 in this region were used to develop an intensity-magnitude-epicentral distance attenuation relationship and the intensity magnitude MI is calibrated to Ms, the surface wave's magnitude. The intensity attenuation relation predicts that, with the same earthquake magnitude, the intensity decrease rate with distance in this region is about 50 percent of predicted from California intensity attenuation model which was developed by Bakun and Wentworth. Based on the intensity attenuation model, we have proposed the Grid Searching of Trial Source Location (GSTSL) method for estimating earthquake magnitude and bounding epicentral region from the calculation of confidence value of rms[MI]=rms(MI-Mi)-rms0(MI-Mi) and the contours of MI=mean(Mi), where rms is the root means square, rms0(MI-Mi) is the minimum rms over a grid of assumed epicenter, and Mi (i=1, 2, 3,¡) are the discrete values derived from the intensity attenuation model. Furthermore, we have discussed the size effect of b-value, a parameter used in Wi of weight function in order to precisely compute rms[MI], on the closure of rms[MI] contours. Finally, in order to demonstrate the technical strategy we have developed in estimating historical earthquake magnitude and bounding its epicentral region, four typical earthquakes are used in our analysis, which include 1668 Juxian-Tanchen event, 1679 Sanhe-Pinggu event, 1966 Longyao event and 1969 Bohai event. The results show that, by minimizing earthquake magnitude within the 90 percent confidence region of rms[MI], the intensity magnitudes of MI are 8.8, 7.8, 6.8 and 7.4 for these four events, respectively. It needs to point out that the technique we have developed here also can be used for bounding the epicentral region and earthquake magnitude in other regions with abundant historical earthquake documents in China.
S13C-1813
Attenuation Relationship of Arias Intensity for Taiwan
Arias intensity (AI) reflects the complete acceleration time history duration of ground vibrations. It correlates well with several commonly used demand measure of structural performance, liquefaction, and seismic slope stability. A good attenuation equation can reflect the characteristics of the ground-motion attenuation for a region, and can be used to predict the ground-motion value of a specific site for seismic resistance design. This study analyzed two local empirical attenuation relationships, one for the crustal earthquakes and the other for the subduction zone earthquakes, based on the strong ground-motion data from TSMIP and SMART1 array in Taiwan. Maximum likelihood method and mixed-effect model were used with non-linear regression analyses to determine coefficients. The result shows that adding terms of Vs30 and focal mechanism can effectively reduce the standard deviation in the attenuation models. To compare with other AI attenuation equations, the AI value predicted by our crustal earthquake attenuation equation is higher in the near field and is lower in the far field than the researches in other regions. The subduction zone earthquake attenuation equation predicts higher AI value than the crustal earthquake attenuation equation does.
S13C-1814
Preliminary Site Classification using the Geologic Map of the Korean Peninsula
Studies of the earthquake ground motion consider the soil properties or the bed rock properties in the upper 30 m. The average shear wave velocity in the upper 30 m defined from borehole data is routinely used for classifying the site conditions. However, it is difficult to classify the site condition using the limited borehole data to cover the whole Korean Peninsula. In the study of Lee et al. (2001), site classification of Taiwan was refined using surface geology from the geologic map, geomorphologic data, and borehole data following the guidelines of National Earthquake Reduction Program (NEHRP). Wald and Allen (2007) defined shear wave velocity using slope of topography or gradient in global scale. They also compared their results in the Taiwan region to those proposed by Lee et al. (2001). In this study, we used geologic map, geomorphologic data, estimated average shear wave velocity from slope of topography, and borehole data to define the site conditions of the Korean Peninsula. We compared our results to the borehole data or seismic site condition data which include seismometer locations and ground conditions. There are some differences between our results and seismic site condition data. The discrepancy is attributed to the relatively large scale geologic map (1:250000) which may not include accurate site condition of the regions. Estimated site conditions of the study, however, agree with those from borehole data when a 1-mile buffering distance is applied to geologic condition boundaries. These results provide useful information for the further study of regional hazard estimation, risk management, and other seismological and geotechnical applications.
S13C-1815
An Application of the Fault Rupture Model for Probabilistic Earthquake Hazard Analysis
The fault rupture model is applied to probabilistic earthquake hazard analysis of back ground seismicity. The aim of this study is introducing effects of minute source condition to the probabilistic hazard analysis. Because average ground motion derived from empirical models are only employed in the probabilistic analysis. The empirical attenuation formulae have advantage for giving ground motion characteristics with empirical uncertainties. However the uncertainties contain source dependent randomness and fluctuations caused by not only source but also path and site effects without separation. The effects can be treated separately by the fault rupture model. Applying the fault rupture model, we expect that we can estimate more natural earthquake hazard from background seismicity than estimation by empirical method. Thousands of fault rupture models are randomly generated introducing variations of strike and dip angles, fault rupture and asperity areas, stress drop, rupture velocity, rupture duration, locations of asperities and rupture starting point and so on. The fault models are generated around a target site with variable magnitudes (Mw 5.5 - 7.0) and corresponding fault lengths. Amount of earthquakes with individual magnitude is controlled by introducing b-value. Strong ground motions from the models are calculated by using stochastic Greenfs function method. Response spectra of calculated ground motions are successfully compared with those by an empirical attenuation technique especially in short period range. However, in period range longer than one second, ground motions by the fault rupture model have larger variation than those by empirical method, because of rupture directivity effect. The advantage and disadvantage for applying fault rupture model to probabilistic earthquake hazard analysis are discussed using the data base of calculated ground motions.
S13C-1816
Characterization of Heterogeneous Source Model of Intraslab Earthquakes Toward Strong Ground Motion Prediction
Since Japanese Islands are located along the subduction zone, large intraslab earthquakes that occurred within subducting slabs generated earthquake disaster (e.g., the 1993 Kushiro-oki earthquake, the 2001 Geiyo earthquake, and the 2003 Miyagi-oki earthquake). It is necessary to construct characterized source model for reliable strong motion prediction of intraslab earthquakes. Somerville et al. (1999) compiled the kinematic source models and proposed a set of empirical scaling relationships for inland crustal earthquakes. Murotani et al. (2008) proposed empirical scaling relationships for plate-boundary earthquakes. Mai and Beroza (2000) also studied scaling properties of kinematic source models. We started to compile kinematic source models of intraslab earthquakes to compare source scaling properties with those of inland crustal and subduction-zone plate-boundary earthquakes. At first, we characterized these heterogeneous slip distributions and extracted rupture area, asperity, and average slip following the procedure proposed by Somerville et al. (1999) to see general nature of source models for these intraslab earthquakes. We also collected SMGA (strong motion generation area, Miyake et al., 2003) source models by the studies on broadband strong ground motion simulation using the empirical Green's function method for intraslab earthquakes (e.g., Asano et al., 2003, 2004; Morikawa and Sasatani, 2004) to compare with the heterogeneous source slip models by waveform inversion. From the seven event source models (Mw 6.6- 7.7), the average size of total rupture area and combined area of asperities of intraslab earthquakes are 67% and 46% of those of crustal earthquakes under the same seismic moment. The ratio of the combined area of asperities to the total rupture area is 9-21% and it is almost the same for the crustal events. We also find that the stress drops on the asperity area shows 10-65MPa, which are larger than those of inland crustal earthquakes. The SMGAs coincide to the asperity area for the 2003 Miyagi-Oki, and the 2001 Geiyo earthquakes. The characterized source model for intraslab earthquakes will be discussed. Acknowledgments: This study is supported by the Special Project for Earthquake Disaster Mitigation in Metropolitan Tokyo Area of MEXT.
S13C-1817
Stochastic Strong Ground Motion Simulation of the 12 November 1999 Duzce (Turkey) Earthquake: Correlation Between Observed Damage and Ground Motion Distribution
The stochastic finite-fault technique is used to simulate strong ground motions of the 12 November 1999 Duzce (Turkey) earthquake. In this method, originally proposed by Beresnev and Atkinson (1997), the finite- fault plane is discretized into a number of rectangular subfaults, each of which is treated as a stochastic point source with an w-square spectrum. The contribution from each subfault is lagged and summed at the observation point. Ground motion simulations are carried out using regional model parameters as well as local soil conditions. Model parameters are calibrated against the strong ground motion recordings of the 1999 Duzce earthquake. Results are expressed in terms of the simulated acceleration and velocity time histories, Fourier amplitude spectra and response spectra. Finally, a regional simulation using the calibrated model parameters is performed and ground motion parameter maps (e.g.: peak ground acceleration and spectral acceleration maps) are generated including the regions where there are sparse or no ground motion records. Through these maps, the spatial distributions of ground motion parameters are correlated with the observed structural damage during the 1999 Duzce earthquake.
S13C-1818
Detailed Distribution and the Topographical and Geological Factors of builiding Damage caused by the Earthquake: Case study of the Noto Hanto Earthquake in 2007 and the Niigataken Chuetsu-oki Earthquake in 2007
Most of researches about a relationship between the seismic damage on the building and topography and geology were concluded by just verifying the fact that the severe building damage area is corresponded to the soft ground area. The researches focusing the difference of building damage from the viewpoints of topography and geology haven't been established yet. It could be difficult to argue that the current forecast of seismic ground motions helps the disaster prevention in a practical level. Therefore, from the standpoints of topography and geology, this research aims to analyse the relationship between difference of building type and extent of damage. This research examined the seismic damage of every building in relatively small area caused by the Noto Hanto Earthquake in 2007 and the Niigataken Chuetsu-Oki Earthquake in 2007. This close investigation could exclude the influence of the attenuation and make possible to discuss about the relationship between building damage and topographical and geological conditions with high resolution. The degree of building damage was classified based on the extent of building damage from A into F in heavy the order. Attributes of the building, such as the purpose of building, stratification, form of the roof and the established age were also considered. Analyses of the topographical and geological condition were presumed by using the micro-topography classification, the existing boring data and the microtremor observation. Those data were superposed by using Geographic Information System (GIS) in order to examine the tendency and primary causes of the building damage. In the case of the Noto-Hanto Earthquake in 2007, the study area covered around 0.3 kilometer square of Hashiride-district, Monzen-town, Wajima city, Ishikawa prefecture where seismic intensity 6+ in the Japan Meteorological Agency (JMA) scale was observed. The seriously damaged area was on the left side of the Oniya-river. In addition, by analysing the boring data and the difference of predominant period of ground by microtremor observation, it could be suggested that the building damage was influenced by local topographical and geological conditions. In the case of the Niigataken Chuetsu-Oki earthquake in 2007, the study area covered around 0.15 kilometer square of the boundary between alluvial plain and sand dune in Kashiwazaki urban area where seismic intensity 6+ in JMA scale was observed. In fact, damage of the 279 detached houses among these became more serious from the borders between alluvial plain and sand dune northward. One of the possible causes of the increased building damage in Niigataken Chuetsu-Oki earthquake could be the lateral spread of sand dune. As can be seen from the fact that no specific change were found in the subsurface structure by analysing the boring data and microtremor observation, most of the building damages could be caused by the influence of the surface layer. We could prove that, even in the relatively small areas, the extent of building damage caused by the earthquake is influenced by the conditions of micro-topography and subsurface structures. Besides, as the extent of building damage was not the same in the area that has similar conditions of micro-topography and subsurface structure, other factors such as the established age and structure of the building could be also influential to the building damage. Therefore, it could be argued that this research helped to establish more accurate, practical forecast and measures of damage caused by earthquake.
S13C-1819
Sensitivity of Probabilistic Ground Motion and its Deaggregation to Different Values of Aperiodicity Parameters in Time Dependent Occurrence in the Central Apennines, Italy
We show the effect of time-dependence, using BPT (Brownian Passage Time) and time–independent Poisson models on the ground motion hazard in the Central Apennines, Italy. Using a characteristic earthquake model for the fault, we produce probabilistic seismic hazard assessment (PSHA) maps for peak ground acceleration (PGA) and 1.0-Hz spectral acceleration (SA1) on rock having 10percent probability of exceedence in 50 years. To show sensitivity to the occurrence models, we generate ratio maps between different models, using different aperiodicity parameters (0.3, 0.5 and 0.7). We also produce several hazard curves and deaggregation plots for some specific sites. In deaggregation for these sites, when we examine the dominating sources, fault sources which might be candidates for deterministic design ground motions, gain or lose influence under time-dependence depending on whether the elapsed time is short or long compared to average recurrence time. The role of the high-rate or low-rate background seismicity adds additional unpredictability. In fact, we see all of following behaviors with decreasing aperiodicity, and list the likely behaviors of the dominating fault (DF) at the selected sites at frequency, a) Hazard increases continuously: DF has elapsed time greater than the average recurrence interval at the site; b) Hazard decreases and then levels off: Influence of DF having elapsed time shorter than average recurrence interval decreases to the point where the background seismicity dominates; c) Hazard maintains a steady level: background seismicity always dominates; d) Hazard stays level and then increases: background seismicity loses domination to a fault with elapsed time longer than the average recurrence interval; e) Hazard stays level and then decreases: DF has elapsed time shorter than average recurrence interval; f) Hazard decreases and then increases: initially DF has recurrence time shorter than the average recurrence interval, but then loses domination to another fault having elapsed time longer than average recurrence interval; g) Hazard increases and then decreases: DF has elapsed time near 0.6 times the average recurrence time, a value where the probability of occurrence increases and then decreases as aperiodicity goes from 0.7 to 0.5 to 0.3. This complex behavior of hazard and its dominating sources suggests that when determining design ground motions, examination of the effect of time-dependence is a necessary adjunct to deaggregation.
S13C-1820
A NEHRP Site Class Map for the Island of Hawaii
As demonstrated in the 2006 M 6.7 Kiholo Bay earthquake, where some strong motion stations recorded peak horizontal accelerations close to 1g, site response effects can be significant on the Big Island. As part of FEMA-supported studies following the earthquake, we have produced a new 1:100,000-scale map of site conditions for the Big Island of Hawaii. The mapping makes use of about 25 new SASW measurements (Wong et al., 2008) and 1:100,000-scale geologic mapping by Sherrod et al. (2007). An earlier 2006 site class map portrayed nearly all of the island as NEHRP site class B; however, based on about 20 SASW measurements in areas mapped as basalt, we believe that most of the island should be mapped as NEHRP C or D. Vs30 estimates for these basalt sites ranged from 844 to 1,812 ft/sec, spanning NEHRP classes C and D. The median value for these Vs30 estimates is 1,304 ft/sec, with a log mean of 1,274 ft/sec and a standard deviation of 274 ft/sec. The sites cover a range of basaltic rock conditions as depicted on the geologic map, including lava flows, scoria cones, littoral deposits, spatter or tuff cones, cinder cones, and lava domes. Other geologic map unit groups for which only a few Vs30 estimates were made from SASW data include alluvium, ash/tephra, and artificial fill. We assign to these map units NEHRP site class D?, C to E, and C to E, respectively. Geologic deposits for which we do not have quantitative velocity data and have made preliminary site class assignments are sand dunes (D?), landslide deposits (D?), and glacial deposits (D?). We also attempted to relate Vs30 estimates to mapped pedogenic soil units, ages of mapped basalt units, and source volcanoes for basalt units, but found little basis for making these correlations. This new map will be incorporated into ShakeMap and HAZUS, which are operational on the Big Island.
S13C-1821
In-situ Seafloor Sediment Characterization From Background Noise and Earthquakes Recorded in the Gulf of California
We present an in-situ evaluation of the response of the Gulf of California (GoC) seafloor sediments to passive dynamic loads. Horizontal-to-vertical (H/V) spectral ratios are used to characterize the local seafloor sediment response in terms of the distribution of ground motions with their respective resonant frequencies. Ambient noise, local and regional earthquakes are used as passive dynamic loads. An analysis and description of the GoC seafloor background noise is also presented. The data was recorded by fourteen stations with three-component broadband sensors and a differential pressure gauge (Ocean Bottom Seismograph, OBS) of the Sea of Cortez Ocean-Bottom Array (SCoOBA) seismic experiment. Earthquakes and other natural seismic signals were recorded for nearly 12 months between October 2005 and October 2006. High frequency local events with impulsive onset arrivals as well as emergent onset arrivals are frequent on all stations. Earthquakes from regional and teleseismic distances are abundant and well defined on several stations simultaneously. The background noise clearly shows changes of the noise levels at intervals of approximately 6 hours in long period signals. Two sub-arrays were centered within the Alarcon and Guaymas basins, ~20 km spacing, and four additional instruments were deployed at ~100 km spacing. The array successfully recorded micro- seismic activity, dozens of local events, M > 3.5, and two large (M ~ 6) events with numerous foreshocks and aftershocks. The H/V spectral ratio technique offers a fast and inexpensive means to obtain information of the preferential vibration modes of soft sediment systems. This information is useful for the design of marine structures because makes use of background noise and earthquake signals. The main advantage is that there is no need for active sources to conduct the study. The method is also well suited for modeling shallow sediments, which usually cover most of the seafloor. H/V spectral ratios were computed for all signals and compared between each other to characterize the effect of the seafloor marine sediments on the seismic records.
S13C-1822
Site Amplification Characteristics of Several Seismic Stations within the Korean Peninsula
The horizontal to vertical (H/V) ratio technique in spectral domain is a common useful technique to estimate empirical site transfer function. The technique, originally proposed by Nakamura(1989), is proposed to analyse the surface waves in the micortremor records. The purpose of this paper is to estimate spectral ratio using observed data at the seismic stations distributed within Southern Korean Peninsula from the Fukuoka earthquake series including 11 aftershocks, recorded at distances from 150 to 500km. The local magnitudes ranges are from 3.9 to 6.5. The results show that most of the stations have fairly reasonable amplification characteristics in low frequency band. However, some of the seismic stations show one (resonant frequency specific to the site) to several local narrow peaks of amplification at high frequency bands. Using these site amplification characteristics,the parameters of seismic source and crustal path attenuation can be estimated more recisely within Southern Korean Peninsula and also can be used to site investigation of the nuclear power plant sites and the nuclear waste stie.
S13C-1823
Paleoseismological study on stone cultural sites in Gyeongju, SE Korea
The Korean peninsular, located within the Eurasian intracontinental region, is presently considered to be tectonically safe compared with neighboring countries such as Japan and Taiwan. However, historical records for the Gyeongju area, which is an old capital city with many ancient stone buildings, demonstrate that seismic events have significantly affected lives and properties in this town. For example, one reported earthquake in 779 AD had an inferred magnitude of M=6.7 and resulted in the deaths of over a hundred people and the destruction of many buildings. This study examines the affects of paleoseismological events recorded by stone constructions in Gyeongju. The study area contains mostly granite and is located near the junction between the Yangsan and Ulsan faults, which represent two of the major faults in SE Korea. In May of 2007, a statue of Buddha that was previously attached to and carved from a vertical granite cliff was discovered resting on the 45¢®¨¡ slope of the Yeolam valley. Based on the artistic style of the granite statue, it was estimated to be during the late 8th century; it has a weight of about 70 tons and dimensions of 250x190x620 cm. Four main joint directions exist in the statue and in granite exposed in the cliff at its original location. These joint sets match if the statue were rotated 15¢®¨¡ clockwise back from present position. Another evidence for damages also occurs at ChumSungDae astronomical observatory. One possible cause for these destructions and damages is paleoseismicity in this area.
S13C-1824
Monitoring Some Seattle Landmarks
We have placed instruments in the UW (formerly SafeCo) Tower and on the Alaska Way Viaduct in Seattle to monitor their motions. Monitoring conventionally provides information on site response and real time measurements of shaking during earthquakes. We are also investigating the possibility of monitoring the fundamental modes of the structures as a proxy for structural integrity and, if we are unlucky enough to capture sufficiently strong shaking, the possibility of trying to correlation damage with high-frequency transients. Using four instruments located at the corners of the top floor, we identify the fundamental modes and first overtones for bending in the N-S direction, in the E-W direction, and in torsion hourly for 200 days. The building has 22 floors and a rectangular footprint with the N-S dimension being slightly greater than the E-W dimension. We compared the fundamental modes with temperature, precipitation, wind speed, and humidity. In the N-S direction the frequency of the fundamental mode is 0.53 Hz, in the E-W direction, 0.48 Hz, and in torsion, 0.64 Hz. Higher modes are also visible but not yet identified. Variations in the modes are highly coherent. The variations about the mean of the coherent parts of the three fundamental modes are about 0.7%, while the variations of the non-coherent parts are about 1.3%, 1.2%, and 1.6% for N-S, E-W, and torsion, respectively. The torsional mode is the most variable, indicating greater variation in shear properties. Of all the weather data, only the amount of rainfall appears to consistently affect the fundamental modes, reducing their frequency. This may be due to a reduction in shear strength of the soils around the foundation of the structure. Instrumentation on the Alaska Way Viaduct was just plugged in a week prior to writing this abstract. We will analyze its motions in a similar manner. Initial review reveals a fascinating menagerie of modes and traffic transient motions.
S13C-1825
Changes in Seismic Response of the Natural Resources Building, Olympia, WA Due to Earthquake Shaking
The Natural Resources Building (NRB) in Olympia was shaken by three earthquakes (Mw=5.8, 6.8, and 5.0) between 1999 and 2001. Building motions were recorded on digital accelerographs, which comprise one of the best dense digital recordings to date of repeated strong shaking an a building. N-S motions dominate the fundamental mode of vibration of the building. In the 1999 earthquake, the frequency of this fundamental mode was 1.3Hz during motions of 10%g. The frequency dropped to 0.7Hz during the 2001 Nisqually strong motions, in which the strongest shaking included high-frequency transients of up to 0.18 g, several of which are visible on widely spaced stations. The weaker 2001 Satsop earthquake motions showed the frequency remained depressed at less than 1Hz for the eastern side of the structure, although the western side had recovered to 1.3Hz. An ambient noise survey in 2008 showed the fundamental frequency of N/S vibrations remains about 1.0Hz for the eastern side of the building and 1.3Hz for the western side. These results suggest that in the Nisqually earthquake, the east side of the NRB suffered a permanent reduction in fundamental mode frequency of 37% due to loss of stiffness by undetermined mechanism.
S13C-1826
Automated and Rapid Determinations of Earthquake Source Parameters in Indonesia: Comparisons with Global CMT Solutions
Rapid determinations of the earthquake source parameters are important for early disaster response and tsunami warning issue. After the devastation of the 2004 great Sumatra-Andaman earthquake, a nationwide broadband seismograph network in Indonesia has been developed by international cooperations among Meteorological and Geophysical Agency of Indonesia (BMG), GeoForschungsZentrum Potsdam, Germany (GFZ), the China Earthquake Administration (CEA), and the National Research Institute for Earth Science and Disaster Prevention, Japan (NIED). This seismic network is intended to improve the capabilities for monitoring seismic activity and tsunami generation in Indonesia, and is a part of the Indonesia Tsunami Early Warning System (InaTEWS). We developed an automated system for rapid determinations of the earthquake source parameters called SWIFT (Source parameter determinations based on Waveform Inversion of Fourier Transformed seismograms) using data from the seismic network in Indonesia. This paper describes the SWIFT system and its performance. We also compare the obtained source parameters with those obtained by the Global Centroid Moment Tensor (GCMT) project (http://www.globalcmt.org/). The SWIFT system is based on the waveform inversion method of Nakano et al. (2008, GJI, 173, 1000-1011). In this method, waveform inversion is carried out in the frequency domain to rapidly and routinely estimate both the focal mechanism and moment function. A pure double-couple focal mechanism from a point source is assumed in order to stabilize the inversion using data from a small number of seismic stations. The fault and slip orientation angles are estimated by a grid search with respect to the dip, strike, and rake angles. The source centroid location is determined by a spatial grid search, in which we adopt adaptive grid spacings for an efficient search. The moment function is reconstructed from its bandpassed form obtained from the inversion. This system is triggered by receiving initial hypocenter information from the GEOFON email alert. Using the displacement seismograms with a total length of 512 s and Green's functions stored in a library, the inversion is performed to estimate the source parameters. Finally, when the result is judged sufficiently accurate, the estimated source parameters are displayed on our web server (http://www.isn.bosai.go.jp/en/index.html). Using the inversion method, we created a CMT catalogue for earthquakes in Indonesia that occurred between July 2006 and May 2008. We obtained CMT solutions for 180 earthquakes with the moment magnitude larger than 5. We compared the source parameters with those obtained by the GCMT project. The average differences in the horizontal source location and depth are 40.7 km and -5.6 km, respectively. The horizontal difference corresponds to twice the grid spacing of the grid search. The moment magnitudes obtained by our method are almost identical to those estimated by the GCMT project. These results indicate that our CMT solutions are consistent with those obtained by the GCMT project. The average time required for the source parameter estimations by this system is 13 minutes after the occurrence of earthquakes, which is much shorter than that required for CMT estimations based on global seismic networks. Seismic monitoring based on our inversion system provides early notification of detailed characterizations of earthquakes including the moment function, which may be useful for identification of tsunami earthquakes and can provide supporting information for tsunami warnings.
S13C-1827
A relation between Mjma and seismic moment (determined from dense broad band seismograph network) for shallow crustal events in Japan
Relation between local magnitude and seismic moment Mo is very important issue on modeling of source
characteristics as well as prediction of strong ground motion.However, existing relations are determined
statistically from limited records.In Japan, a local magnitude Mjma is announced systematically by Japan
Meteorological Agency.Takemura et al.(1990,1998)determined empirical relations between Mjma and Mo for
crustal earthquakes, and Fukushima (1998) derived a semi-empirical relation based on available data up to
their publication.Strong motion is strongly depending on source modeling, nevertheless, Mo for specific
magnitude is still estimated with those relations.
Nowadays in Japan, high density broad band seismograph network is already installed by National Research
Institute for Earth Science and Disaster Prevention(NIED),and moment tensor solutions are also
systematically announced through their web site.We determined an empirical relation between Mjma and Mo
with data announced by the both organizations. Data are selected from October 1997 up to last July and
Mjma less than 4 are omitted.This region is locating on a confusing tectonic regime,and different strong
motion characteristics can be expected for individual source types such as crustal, inter plate and slab
events.In this study,we focus on shallow crustal events,since extremely strong motion is estimated at close
distance from source of crustal events.
In order to avoid influence of earthquake swarm,fore- and after-shocks,we eliminated them with relation
between their spatial distribution and Mjma inspected by Public Works Research Institute, Japan.Total of 350
data from crustal events were selected, and a following relation was determined by regression analysis,
log10Mo(N·m)=1.40Mjma+9.42(1)
On the other hand, Harvard CMT solution has been already used from 1978 worldwide. Estimated Mo by F-
net is systematically smaller than that of Harvard CMT in smaller Mw than 5.5(Kubo et al.,
2001).Therefore,we eliminated Mjma less than 5.8 corresponding to Mw 5.5 by equation (1) and recalculated
a following relation with 20 remained events.
log10 Mo(N·m)=1.34Mjma +9.62
This result was compared with several other relations of Takemura(1990,1998)and Fukushima (1998) of a
classical equation. Our result agrees well with Fukushima (1998) from 5.5 to 6.0 of Mjma maybe due to
reliability of the data in this range. On the contrary, Takemura's relations are also focusing on crustal events,
so our result are well corresponding to them particularly above Mjma greater than 7, although this range is
not enough constrained by the observed data.
Determined equation between Mjma and Mo in this study is
based on advanced data, and agree well with former relations. With this equation, conversion from Mjma to
Mo can be facilitated. It is quite obvious that Mo is more physical parameter than the local magnitude for the
estimation of strong ground motion. The converted Mo from Mjma will be able to apply on source modeling of
crustal events, and used for predictions of strong ground motion with empirical attenuation relations of Mw
as a parameter. Although quantitative and qualitative data are observed in Japan, discontinuity between
Mjma and other scales is blocking universal use,. With this result, we wish that Japanese local data will be
available for world wide application.
S13C-1828
Magnitude scaling relationships from the first 3 seconds of P-wave arrivals in South Korea
We studied an empirical magnitude relationship for South Korea using 29 earthquakes observed on KMA (Korea Meteorological Administration) seismic network between 2001 and 2007. We selected events whose magnitudes were greater than ML 3.0 and located inside the KMA seismic network. To determine the scaling relationships of period magnitude and amplitude magnitude, we calculated the maximum predominant period (τpmax) and the peak displacement amplitude (Pd) calculated from the first 3-second data of P-wave arrivals on vertical component. The computed magnitude relationships from τpmax and Pd show M = 0.79τpmax - 4.53 and M = 1.24log(Pd) + 1.56log(R) + 5.11 (R = epicentral distance), respectively. Obtained magnitude scaling relationships were utilized to compute an earthquake early warning simulation with the Odaesan (ML = 4.8) earthquake, which is the biggest inland earthquake observed on the modern digital seismic network in South Korea. The simulation results using "ElarmS" with the relationships obtained from this study will be discussed.
S13C-1829
Rupture propagation image during the Niigataken Chuetsu-oki earthquake in 2007 by an array-backprojection approach using near source strong ground motions
The 2007 Niigataken Chuetsu-oki earthquake occurred near the Kashiwazaki-Kariwa nuclear power plant in Japan, the largest in the world. The strong motions were recorded by seven seismometers installed at the foundation slab (base-mat) of the plant, and exceeded the design level of the ground motion for the plant. The strong-motion observed by the seismographs in and around the plant show high-coherency with three significant pulses. In order to understand the cause of these pulses, the rupture process of the earthquake was estimated using these seismograms. The seismograph network was taken into account as a dense array and semblance-enhanced waveform stacking was performed. By projecting the power of the stacked waveforms on to the fault plane, the asperities that generated significant pulses were successfully separated. The first and third pulses were generated at the hypocenter and the southwest edge of the rupture zone, respectively. The ruptured area expanded to the southwest of the fault plane and terminated offshore from the power plant. The rupture started at the hypocenter and unilaterally propagated toward the southwest.The rupture propagation velocity estimated by the least square method was approximately 2450 m/s. The rupture velocity near the hypocenter appeared to be faster than that of the distant part. This implies a complex rupture process on the fault plane. Our results clearly show that analyses using array data provide an effective way for imaging rupture propagation and determining asperity locations as the source of coherent waves, even in the case of a M7 class earthquake. In addition, even in the case of a thick sedimentary layer, which may mislead results of waveform inversions, or in the case of rupture velocity variations on the fault plane, the back-projection method can be a useful tool to obtain the rupture process.
S13C-1830
Application of Rapid Earthquake Location for Earthquake Early Warning in Korea
Economic growth, industrialization and urbanization have made society more vulnerable then ever to seismic hazard in Korea. Although Korea has not experienced severe damage due to earthquakes during the last few decades, there is little doubt of the potential for large earthquakes in Korea as documented in the historical literature. As we see no immediate promise of short-term earthquake prediction with current science and technology, earthquake early warning systems attract more and more attention as a practical measure to mitigate damage from earthquakes. Earthquake early warning systems provide a few seconds to tens of seconds of warning time before the onset of strong ground shaking. To achieve rapid earthquake location, we propose to take full advantage of information from existing seismic networks; by using P wave arrival times at two nearest stations from the earthquake hypocenter and also information that P waves have not yet arrived at other stations. Ten earthquakes in the Korean peninsula and its vicinity are selected for the feasibility study. We observed that location results are not reliable when earthquakes occur outside of the seismic network. Earthquakes inside the seismic network, however, can be located very rapidly for the purpose of earthquake early warning. Seoul metropolitan area may secure 10 – 50 seconds of warning time before any strong shaking starts for certain events. Carefully orchestrated actions during the given warning time should be able to reduce hazard and mitigate damages due to potentially disastrous earthquakes.
S13C-1831
Performance of Real-time Earthquake Information System in Japan
Horiuchi et al. (2005) developed a real-time earthquake information system (REIS) using Hi-net, a densely deployed nationwide seismic network, which consists of about 800 stations operated by NIED, Japan. REIS determines hypocenter locations and earthquake magnitudes automatically within a few seconds after P waves arrive at the closest station and calculates focal mechanisms within about 15 seconds. Obtained hypocenter parameters are transferred immediately by using XML format to a computer in Japan Meteorological Agency (JMA), who started the service of EEW to special users in June 2005. JMA also developed EEW using 200 stations. The results by the two systems are merged. Among all the first issued EEW reports by both systems, REIS information accounts for about 80 percent. This study examines the rapidity and credibility of REIS by analyzing the 4050 earthquakes which occurred around the Japan Islands since 2005 with magnitude larger than 3.0. REIS re-determines hypocenter parameters every one second according to the revision of waveform data. Here, we discuss only about the results by the first reports. On rapidness, our results show that about 44 percent of the first reports are issued within 5 seconds after the P waves arrives at the closest stations. Note that this 5-second time window includes time delay due to data package and transmission delay of about 2 seconds. REIS waits till two stations detect P waves for events in the network but four stations outside the network so as to get reliable solutions. For earthquakes with hypocentral distance less than 100km, 55 percent of earthquakes are warned in 5 seconds and 87 percent are warned in 10 seconds. Most of events having long time delay are small and triggered by S wave arrivals. About 80 percent of events have difference in epicenter distances less than 20km relative to JMA manually determined locations. Because of the existence of large lateral heterogeneity in seismic velocity, the difference depends on regions and tends to increase when earthquakes occurred outward the network. Depth differences for 70 percent of events are less than 20km and original time differences for 48 percent within one second. In addition to JMA magnitude (MJMA), which is estimated from moment magnitude, REIS estimates a new scaling parameter called intensity magnitude (MI), which is defined from observed P wave seismic intensity (Yamamoto et al., 2008). Our statistical results show that these two kinds of magnitudes are reasonably determined. Either MJMA or MI by REIS for 94 percent of events has differences less than 1.0 compared with reported JMA catalog. However, the difference increases with values of the magnitude. There is an apparent underestimation of MJMA for large earthquakes because the first report is issued when the rupture is still undergoing. Moreover, there are cases when most of Hi-net seismograms close to epicenter are clipped, but still these data are used for the determination of the lower limit of magnitude. We are making an EEWS using real-time strong motion network data for the better estimate of earthquake magnitude and seismic intensity.
S13C-1832
Real-time calculation of seismic intensity used in Japan
Since 1996, the seismic intensity redefined by Japan Meteorological Agency (JMA) has been used in Japan. This seismic intensity (JMA seismic intensity) can be calculated instrumentally from acceleration records and never be determined from human perception or damage investigation. Consequently, the seismic intensity used in Japan completely became an instrumental index. Nowadays the JMA seismic intensities are calculated by thousands of officially approved seismic intensity meters deployed entire region in Japan and the intensities are announced up to about two minutes when a large earthquake occurred. Nevertheless, calculation of the JMA seismic intensity has a real-time delay of several tens seconds, since it needs a filtering procedure for the acceleration records with 60 seconds duration. It was used to not be issue at the beginning, when the seismic intensity was redefined. However, with requirements of earthquake early warning (EEW) system, Prompt calculation of the intensity is necessary, because the predicted seismic intensity has to be announced before arrival of seismic wave, although the seismic intensity can not immediately be calculated just after the arrival due to above processing. In order to solve above problem, we would like to recommend a new calculation scheme for a real-time seismic intensity index (Ir), which is a similar index as the JMA seismic intensity (Ijma). This index, Ir, can be calculated from each time series with a moving time window on real-time and its maximum value, Ia corresponds approximately to the Ijma. Actually, relationship between Ijma and Ia was inspected statistically by quantitative strong motion records, and Ia consists with Ijma in wide intensity range. Even for a small processor installed in strong-motion observations, Calculation of Ir is much faster than the processing Ijma. Therefore, Ir is suitable for using in an EEW system consistent with the JMA seismic intensity.
S13C-1833
Feasibility study of EEW application in Korea
At present, it seems almost impossible to predict where and how much strong a earthquake will happen within very limited time such as two or three days before it occurs. However, the advantage of modern electronic techniques can support us very fast communication tools around nation-wide area so that we can receive P- waves arrival information from seismic stations through communication lines before S-waves strike our living site. This is the key of EEW(Earthquake Early Warning) concept that is under development around world especially including Japan, United State of America, and Taiwan. In this pilot study we proposed the direction for developing Korean Earthquake Early Warning System. Considering the state of the art techniques used in Japan, USA and Taiwan, ElarmS would be more adaptable to Korea since ElarmS can work from the low limit of moderate earthquakes around magnitude 3.5, which would annually happen in Korea. We investigate empirical magnitude scaling relationship for South Korea using 27 events ranging in magnitude from 2.2 to 4.9 recorded by the Korea Institute of Geoscience And Mineral Resources (KIGAM) and the Korea Meteorological Administration (KMA) for 2007. We measure the maximum predominant period and the peak displacement or velocity amplitude from the first 4 seconds of P wave arrivals to derive period-magnitude and amplitude-magnitude scaling relationship, respectively. For the period-magnitude relationship, we find that 10 Hz low-pass filter yields better estimate than 3 Hz. This is because the magnitudes of most events used in this study are too small (<3.0). It is also shown that peak displacement for velocity instruments and peak velocity for accelerometers have their own magnitude scaling relationships, respectively. Thus, for the amplitude-magnitude relationship, like the relationships in northern California, two individual amplitude scaling relationships would be necessary.
S13C-1834
Korea Integrated Seismic Service (KISS) and Real Time Intensity Color Mapping (RTICOM) for Rapid Earthquake Warning System in Korea
Since 2002 Korea Integrated Seismic Service (KISS) has been playing main role in real-time seismic data exchange between different seismic networks operated by four earthquake monitoring institutes: Korea Institute of Geoscience and Mineral Resources (KIGAM), Korea Meteorological Administration (KMA), Korea Electric Power Research Institute (KEPRI), and Korea Institute of Nuclear Safety (KINS). Seismic data from different seismic networks are gathered into the data pool of KISS where clients can receive data in real-time. Before expanding and modernizing of Korean seismic stations, the consortium of the four institutes made the standard criteria of seismic observation such as instrument, data format, and communication protocol for the purpose of integrating seismic networks. More than 150 digital stations (velocity or accelerometer) installed from 1998 to 2008 in Korea could be easily linked to KISS in real time due to the standard criteria. When a big earthquake happens, the observed peak acceleration value can be used as the instrumental intensity on the local site and the distribution of peak accelerations shows roughly the severity of the damaged area. Real Time Intensity Color Mapping (RTICOM) is developed to generate a every second contour map of the nationwide intensity based on the peak acceleration values retrieved through KISS from local stations. RTICOM can be used to rapid evaluation of the intensity and decision making against earthquake damages.
S13C-1835
GEOFON, GITEWS and the Indian Ocean Tsunami Warning System
After the Mw=9.3 Sumatra earthquake of December 26, 2004, which generated a tsunami that affected the
entire Indian Ocean region and caused approximately 230,000 fatalities, the German government funded the
German Indian Ocean Tsunami Early Warning System (GITEWS) Project. The GEOFON group of GFZ
Potsdam was nominated to develop and implement the seismological component of the GITEWS system. This
poster presentation describes the concept of the GITEWS Earthquake Monitoring System (EMS) and reports
on its present status and progress of implementation.
The major challenge for an EMS within a tsunami warning system is to determine earthquake source
parameters in terms of location, size and possibly rupture propagation as quickly as possible, in order to
allow counter measures before a potential tsunami may hit coastal areas. Tsunamigenic earthquakes usually
occur along subduction zones, which are often close to coastal lines. In the Indian Ocean this is particularly
true for the Sunda Trench off the shore of Indonesia and the Macran subduction zone off the shore of Iran.
For an Indian Ocean monitoring system where short warning times are a requirement, a dense real-time
network of seismic stations in Indonesia is therefore essential. It must be supplemented by a substantial
number of stations in other countries surrounding the Indian Ocean. International cooperation and real-time
data exchange across political boundaries are essential for successful tsunami warning in the Indian Ocean
region. Within the GITEWS project, up to 40 new broadband and strong motion stations are being installed
in the Indian Ocean region until 2010. Up to 22 new stations are set up in Indonesia and another 18 stations
distributed over Sri Lanka, Maldives, Yemen, Kenya, Tanzania, Madagascar and Israel. Real-time
communication is provided by private VSAT communication systems.
Another challenging task within the GITEWS project is the design and implementation of efficient and fast
acquisition and processing software. Based on an innovative software architecture and code, the SeisComP
3 software package has evolved from the widely used SeisComP 1 and 2 packages developed earlier by
GEOFON. It combines real-time data acquisition and quality control with automatic procedures to determine
location, depth, magnitudes and other source parameters. Sophisticated alert and visualization tools provide
a variety of front ends. The basic parameter calculation is done fully automatic by the software. Acoustic and
optical alert tools are implemented to guarantee the attention of the seismic experts in the warning center.
Operators can intervene and correct automatic results to accelerate the automatic processing and to improve
location accuracy. Since May 2007, SeisComP 3 is being used as the primary processing software at the
Indonesian Warning Center BMG for tsunami warning purposes.
The current version of the software implements a newly-developed rapid and robust regional magnitude
calculation. Since it installation in Indonesia in early May 2007, SeisComP 3 has provided realistic magnitude
estimates allowing assessment of an earthquake's tsunami potential and possibly warning by BMG in less
than 5 minutes. The SeisComP 3 earthquake monitoring system at BMG is already connected to similar
systems in Germany, the Maldives and the Republic of Yemen, for exchange of seismic waveforms and
earthquake parameters in real-time. Other countries in the Indian Ocean region will follow as soon as data
from their seismic stations become available. There is also interconnection between the GITEWS and the
Northeastern Atlantic and Mediterranean Tsunami Warning System (NEAMTWS).
http://www.gitews.de
S13C-1836
Detection of Land-surface Deformations Associated with Earthquakes from a Satellite- borne Microwave Radiometer Data
Interferograms formed by the data of a satellite-borne synthetic aperture radar (SAR) enables us to detect slight land-surface deformations in connection with volcanic eruptions or earthquakes. However at current, since the time lag between two scenes of SAR used to form interferograms becomes longer than the reccurent period of a satellite aboard it (several tens days), it is not clear enough when land-surface deformations occur in volcanic eruptions or earthquakes. In order to solve this problem, we have investigated another approach to detect land-surface deformations with shorter time resolution from the data of satellite-borne sensors. It was recently confirmed that microwave energy is emitted when rocks are fractured in laboratory experiments. We first extrapolated the experimental results and estimated how much the power of microwave energy generated by rock failures in an earthquake is received by a satellite-borne radiometer. As a result, it was concluded that this microwave energy is detectable enough for a satellite-borne radiometer. Microwave energy can penetrate the ionosphere, so it can be observed by satellite-borne sensors without ionospheric effects, but a large ambiguity exists in the underground propagation of microwaves. This conclusion was obtained under some assumptions for the underground propagation of microwaves. However, if land-surface deformations are detected by SAR, they are accompanied by rock failures. If rocks are crushed by land-surface deformations, the ambiguity in the underground propagation of microwaves is reduced, and microwave energy generated by rock failures becomes increasingly likely to be detected by a satellite-borne microwave radiometer. Based on this concept, we developed an algorithm to evaluate microwave energy generated by rock failures on the land surface. An actual verification of the algorithm was performed by using the data of the Advanced Microwave Scanning Radiometer for Earth Observation System for the earthquake which occurred on May 12, 2008 in Sichuan, China. By the algorithm, we detected definitive microwave signals only one day after the main shock of the Sichuan earthquake during the entire observation period of six years. These microwave signals are highly likely to be associated with phenomena caused by tectonic activities in aftershocks. In this paper, the development process and the verification result of the algorithm is presented.
S13C-1837
Detection of Microwave Frequency Signals from Earthquakes and Volcanic Activities
Microwaves could be used to detect earthquakes and volcanic activities. The principle and concept of the detection system is based on the experimental results that microwave emission was found due to rock failure. It is expected that rock fails in association with earthquakes or volcanic eruptions, and accordingly microwave could be detected in those natural disasters. Particularly, the microwave in a volcanic activity can be detected more easily than that in an earthquake because of the known location and hopefully time, as may be called a canonical problem. First, the detection system of an earthquake microwaves using a satellite in orbit is analyzed to show its availability. Then, the observation of Miyake-jima volcano through microwaves is analyzed and the system is explained. Miyake-jima is an island with an active volcano which erupted in 2004 and forced all inhabitants to evacuate the island. We installed the microwave receiving system there to detect the signals which is emitted from the volcano. In the system, microwave antennas are placed to point the rock cliff of the volcano crater. The output signals are amplified with low noise, then down-converted and detected. Observation is carried out in 300 MHz-, 2GHz- and 18GHz-bands. A seismometer is also installed around the crater. The digitized signals are supplied to data storage and transmission. The observation has been carried out from November 2007 with several interruptions. From the obtained data, several interesting points have been extracted. This paper presents the constitution and characteristics of the volcano observation system, and the obtained data in .more detail.