S14B-01
Transparent Seismic Mitigation for Community Resilience
Healthy communities continuously grow by leveraging their intellectual capital to drive economic development while protecting their cultural heritage. Success, in part, depends on the support of a healthy built environment that is rooted in contemporary urban planning, sustainability and disaster resilience. Planners and policy makers are deeply concerned with all aspects of their communities, including its seismic safety. Their reluctance to implement the latest plans for achieving seismic safety is rooted in a misunderstanding of the hazard they face and the risk it poses to their built environment. Probabilistic lingo and public debate about how big the "big one" will be drives them to resort to their own experience and intuition. There is a fundamental lack of transparency related to what is expected to happen, and it is partially blocking the policy changes that are needed. The solution: craft the message in broad based, usable terms that name the hazard, defines performance, and establishes a set of performance goals that represent the resiliency needed to drive a community's natural ability to rebound from a major seismic event. By using transparent goals and measures with an intuitive vocabulary for both performance and hazard, earthquake professionals, working with the San Francisco Urban Planning and Research Association (SPUR), have defined a level of resiliency that needs to be achieved by the City of San Francisco to assure their response to an event will be manageable and full recovery achievable within three years. Five performance measures for buildings and three for lifeline systems have been defined. Each declares whether people will be safe inside, whether the building will be able to be repaired and whether they will be usable during repairs. Lifeline systems are further defined in terms of the time intervals to restore 90%, 95%, and full service. These transparent categories are used in conjunction with the expected earthquake level to describe the standards needed for new buildings and lifelines and the rehabilitation programs needed for existing buildings and systems. Earthquake professionals -- Emergency Response Planners, Earth Scientists, and Earthquake Engineers – need to embrace this level of transparency and work with their communities to craft the policies needed to instill change and achieve disaster resilience.
S14B-02 INVITED
Space Geodetic Imaging of Earthquake Potential in the San Francisco Bay Area
Active crustal deformation in the San Francisco Bay Area includes contributions from elastic strain buildup across major faults and aseismic fault creep relieving a small portion of the plate tectonic fault slip budget. Increasingly precise and dense measurements of surface motions using GPS and InSAR satellite data provide valuable information on the distribution and rates of surface deformation. In the Eastern Bay Area, the Hayward, Calaveras and Concord faults are known to be source areas of moderate to large earthquakes, but also exhibit significant aseismic fault creep. Modeling of space geodetic data collected along the Hayward fault over > 10-year period allows for the determination of the distribution of currently locked asperities and creeping portions of the fault zone. Inversions of these data reveal a locked zone at depth which has built up a slip deficit since the 1868 Hayward fault rupture that is large enough to produce a M > 6.7 earthquake. The inferred slip rates along the creeping portions of the Hayward fault are significantly less than the long-term slip rate, and thus a substantial slip deficit is accumulating there as well. However, it is possible that the creeping portions of the East Bay faults will catch up most of their slip deficit by accelerated postseismic creep following large ruptures of the currently locked asperities. The kinematic locking models help inform dynamic rupture scenarios and ground motion simulations of major earthquakes along the Hayward fault (Aagaard et al., 2008 Fall AGU).
S14B-03
Geodetically-inferred Coseismic and Postseismic Slip Due to the 31 October 2007 M 5.4 Alum Rock Earthquake: Implications for Fault Characteristics and Earthquake Hazard
Understanding the interaction between the Calaveras Fault (CF) and Hayward Fault (HF) is important to assessing earthquake hazard in the eastern San Francisco Bay region. Recent studies (e.g., Manaker et al., 2005) suggest that at depth the HF connects with the central CF via a simple continuous surface illuminated by the Mission Seismicity Trend (MST). If true, this implies that a damaging earthquake rupture could involve both faults (e.g., Graymer et al., 2007). The 31 October 2007 M 5.4 Alum Rock earthquake on the CF produced coseismic and postseismic displacements recorded by ten continuously operating Global Positioning System (GPS) instruments. The spatial distribution of slip inferred by inverting the GPS data is poorly constrained but compatible with models in which moderate earthquakes on the CF rupture locked patches at depth surrounded by areas that experience creep, afterslip, and microseismicity (Oppenheimer et al., 1990). The magnitude of the coseismic offsets and cumulative postseismic displacements after four months are comparable; constraining the postseismic moment to not exceed the seismic moment degrades the fit to the postseismic data at several sites. The cumulative postseismic displacement and number of aftershocks over time are linearly related, as would be predicted if these phenomena arose from the same underlying process (Perfettini and Avouac, 2004). The GPS data are fit better by allowing, in addition to afterslip at seismogenic depths, localized right lateral/reverse slip on dipping shallow fault surfaces SW of the CF which may be the shallow manifestation of the restraining HF-CF junction, (Watt et al., 2008). If the HF and CF connect at depth via a surface that follows the MST, the combined coseismic and postseismic slip inferred from the GPS data predicts static Coulomb stress increases of ~0.6 bar on this surface and on the northern CF ~5 km NW of the Alum Rock hypocenter. A stress increase of ~0.15 bar is predicted near the SE end of the 1868 Hayward earthquake surface rupture projected downdip to the MST. Alternatively, if the HF is an essentially vertical surface beneath the 1868 surface rupture, a ~0.2 bar stress decrease is predicted at its SE end.
S14B-04
Earthquake and Tsunami planning, outreach and awareness in Humboldt County, California
Humboldt County has the longest coastline in California and is one of the most seismically active areas of the state. It is at risk from earthquakes located on and offshore and from tsunamis generated locally from faults associated with the Cascadia subduction zone (CSZ), other regional fault systems, and from distant sources elsewhere in the Pacific. In 1995 the California Division of Mines and Geology published the first earthquake scenario to include both strong ground shaking effects and a tsunami. As a result of the scenario, the Redwood Coast Tsunami Work Group (RCTWG), an organization of representatives from government agencies, tribes, service groups, academia and the private sector from the three northern coastal California counties, was formed in 1996 to coordinate and promote earthquake and tsunami hazard awareness and mitigation. The RCTWG and its member agencies have sponsored a variety of projects including education/outreach products and programs, tsunami hazard mapping, signage and siren planning, and has sponsored an Earthquake – Tsunami Education Room at the Humboldt County fair for the past eleven years. Three editions of Living on Shaky Ground an earthquake-tsunami preparedness magazine for California's North Coast, have been published since 1993 and a fourth is due to be published in fall 2008. In 2007, Humboldt County was the first region in the country to participate in a tsunami training exercise at FEMA's Emergency Management Institute in Emmitsburg, MD and the first area in California to conduct a full-scale tsunami evacuation drill. The County has conducted numerous multi-agency, multi-discipline coordinated exercises using county-wide tsunami response plan. Two Humboldt County communities were recognized as TsunamiReady by the National Weather Service in 2007. Over 300 tsunami hazard zone signs have been posted in Humboldt County since March 2008. Six assessment surveys from 1993 to 2006 have tracked preparedness actions and personal awareness of earthquake and tsunami hazards in the county and additional surveys have tracked public awareness and tourist concerns about tsunami hazard signs. Over the thirteen year period covered by the surveys, the percent with houses secured to foundations has increased from 58 to 80 percent, respondents aware of a local tsunami hazard increased from 51 to 73 percent and knowing what the Cascadia subduction zone is from 16 to 42 percent.
S14B-05
Earthquake early warning in California: Evaluating Hardware and Software
Three earthquake early warning (EEW) algorithms are currently being evaluated within the California
Integrated Seismic Network (CISN) with support from the US Geological Survey. The evaluation encompasses
two aspects: their operation using data from throughout the state under real time conditions, and
assessment of their alerts at a web-accessible testing center. An EEW system rapidly detects the initiation of
earthquakes and predicts their ground shaking. Its purpose is to provide warning of potentially damaging
ground motion in a target region before the strong shaking arrives. One of the three algorithms implemented
at the CISN data centers uses a single station, or 'On-site' approach (Caltech). The other two, 'ElarmS' (UC
Berkeley) and 'Virtual Seismologist' (VS, Caltech/ETH), are network-based. Although single station alerts can
be delivered more quickly than those from a network-based system, more of them tend to be false warnings.
Network-based algorithms for EEW require that data be gathered at a central site for joint processing. The
two network-based systems, ElarmS and VS, run 15 s behind real time in order to gather ~90% of
station data before processing. The EEW alert testing center was developed by the Southern California
Earthquake Center (SCEC). Results from the various algorithms are collected automatically. Automatically
generated performance summaries allow the comparison of the EEW alerts with each other and with
earthquakes within the region. Performance criteria include promptness of the alert, earthquake location and
magnitude. Provisions have also been made to assess false alerts, ground motion predictions and
uncertainties. In addition to evaluating the three algorithms in terms for separate and joint reliability, we
review the needs of EEW with respect to instrumentation and data latency. Possible warning times will
typically range from seconds to tens of seconds, and each second delay means a decrease in the available
warning time. Minimal latency is therefore important to warning systems. As testing progresses, we are
formulating specifications for geophysical networks that can provide real time data in a robust fashion.
http://www.scec.org/eew/
S14B-06
Earthquake Early Warning for Large Events using Probabilistic Models for Seismic Rupture Prediction
Earthquake Early Warning (EEW) requires a rapid determination of source and ground motion parameters before strong shaking occurs. The potential warning time to heavily shaken areas are greatest for infrequent large earthquakes (Mw>7.5) with rupture expansions of hundreds of kilometers. However, these long rupture-length events pose a major challenge; that is how to recognize that an ongoing rupture is likely to propagate for a long distance. We determine the posterior probabilities of remaining rupture length Lr as a function of current slip amplitude uc from simulated slip pulses using calibrated stochastic 1-D models. We find that (1) large current slip amplitudes usually indicate that a rupture will continue, although the uncertainty is significant which underlines the need for a probabilistic description; and (2) the relationship between uc and Lr is strongly controlled by fault characteristics, such as the spatial roughness of slip along the fault, which may be a function of the maturity of the fault system. For a practical application this means that one of the most important challenges in EEW for large events is the rapid recognition of the characteristics of the fault, along which the rupture propagates. For example, a critical question is, "is this ongoing rupture on the San Andreas fault?"" Our findings also support the hypothesis (with the above constraints) that seismic ruptures are to some degree deterministic, that is magnitudes are statistically predictable within the first few seconds after rupture initiation, provided that the hypocenter is in a patch of large slip.
S14B-07
The 1868 Hayward Earthquake Alliance: A Case Study - Using an Earthquake Anniversary to Promote Earthquake Preparedness
Last October 21st marked the 140th anniversary of the M6.8 1868 Hayward Earthquake, the last damaging earthquake on the southern Hayward Fault. This anniversary was used to help publicize the seismic hazards associated with the fault because: (1) the past five such earthquakes on the Hayward Fault occurred about 140 years apart on average, and (2) the Hayward-Rodgers Creek Fault system is the most likely (with a 31 percent probability) fault in the Bay Area to produce a M6.7 or greater earthquake in the next 30 years. To promote earthquake awareness and preparedness, over 140 public and private agencies and companies and many individual joined the public-private nonprofit 1868 Hayward Earthquake Alliance (1868alliance.org). The Alliance sponsored many activities including a public commemoration at Mission San Jose in Fremont, which survived the 1868 earthquake. This event was followed by an earthquake drill at Bay Area schools involving more than 70,000 students. The anniversary prompted the Silver Sentinel, an earthquake response exercise based on the scenario of an earthquake on the Hayward Fault conducted by Bay Area County Offices of Emergency Services. 60 other public and private agencies also participated in this exercise. The California Seismic Safety Commission and KPIX (CBS affiliate) produced professional videos designed forschool classrooms promoting Drop, Cover, and Hold On. Starting in October 2007, the Alliance and the U.S. Geological Survey held a sequence of press conferences to announce the release of new research on the Hayward Fault as well as new loss estimates for a Hayward Fault earthquake. These included: (1) a ShakeMap for the 1868 Hayward earthquake, (2) a report by the U. S. Bureau of Labor Statistics forecasting the number of employees, employers, and wages predicted to be within areas most strongly shaken by a Hayward Fault earthquake, (3) new estimates of the losses associated with a Hayward Fault earthquake, (4) new ground motion simulations of a Hayward Fault earthquake, (5) a new USGS Fact Sheet about the earthquake and the Hayward Fault, (6) a virtual tour of the 1868 earthquake, and (7) a new online field trip guide to the Hayward Fault using locations accessible by car and public transit. Finally, the California Geological Survey and many other Alliance members sponsored the Third Conference on Earthquake Hazards in the East Bay at CSU East Bay in Hayward for the three days following the 140th anniversary. The 1868 Alliance hopes to commemorate the anniversary of the 1868 Hayward Earthquake every year to maintain and increase public awareness of this fault, the hazards it and other East Bay Faults pose, and the ongoing need for earthquake preparedness and mitigation.
S14B-08 INVITED
Ground Motion Simulations of Scenario Earthquake Ruptures of the Hayward Fault
We compute ground motions in the San Francisco Bay area for a suite of 35 magnitude 6.7--7.2 scenario earthquake ruptures involving the Hayward fault. The suite of scenarios encompasses variability in rupture length, hypocenter, distribution of slip, rupture speed, and rise time. The five rupture lengths include the Hayward fault and portions thereof, as well as combined rupture of the Hayward and Rodgers Creek faults and the Hayward and Calaveras faults. For most rupture lengths, we consider three hypocenters, yielding north-to-south rupture, bilateral rupture, and south-to-north rupture. We also consider multiple random realizations of the slip distribution, accounting for creeping patches (Funning et al., 2007) either through simple assumptions about how creep reduces coseismic slip or a slip-predictable approach. The kinematic rupture models include local variations in rupture speed and use a ray-tracing algorithm to propagate the rupture front. Although we are not attempting to simulate the 1868 Hayward fault earthquake in detail, a few of the scenarios are designed to have source parameters that might be similar to this event. This collaborative effort involves four modeling groups, using different wave propagation codes and domains of various sizes and resolutions, computing long-period (T > 1--2 s) or broadband (T > 0.1 s) synthetic ground motions for overlapping subsets of the suite of scenarios. The simulations incorporate the 3-D geologic structure as described by the USGS 3-D Geologic Model (Jachens et al., 2006; Watt et al., 2007) and USGS Bay Area Velocity Model (Brocher et al., 2007). The simulations illustrate the dramatic increase in intensity of shaking for a magnitude 7.0 bilateral rupture of the entire Hayward fault compared with a magnitude 6.8 bilateral rupture of the southern two-thirds of the fault; the area subjected to shaking stronger than MMI VII increases from about 10% to more than 40% of the San Francisco Bay urban area. For a given rupture length, the synthetic ground motions exhibit the strongest sensitivity to the distribution of slip and proximity to sedimentary basins. The hypocenter also exerts a strong influence on the amplitude of the shaking due to rupture directivity. The synthetic waveforms exhibit a weaker sensitivity to the rupture speed and are relatively insensitive to the rise time.