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Papers by Chris Wills

Earthquake Spectra, 2010

A statistical evaluation of shaking damage to wood-framed houses caused by the 2003 M6.5 San Sime... more A statistical evaluation of shaking damage to wood-framed houses caused by the 2003 M6.5 San Simeon earthquake indicates that both the rate and severity of damage, independent of structure type, are significantly greater on hilltops compared to hill slopes when underlain by Cretaceous or Tertiary sedimentary rocks. This increase in damage is interpreted to be the result of topographic amplification. An increase in the damage rate is found for all structures built on Plio-Pleistocene rocks independent of topographic position, and this is interpreted to be the result of amplified shaking caused by geologic site response. Damage rate and severity to houses built on Tertiary rocks suggest that amplification due to both topographic position and geologic site response may be occurring in these rocks, but effects from other topographic parameters cannot be ruled out. For all geologic and topographic conditions, houses with raised foundations are more frequently damaged than those with slab...

The California Geological Survey (CGS) uses digital mapping techniques to prepare products for a ... more The California Geological Survey (CGS) uses digital mapping techniques to prepare products for a wide variety of users, who range from geologists to engineers to local government planners and the public. In California, almost all land-use planning and building decisions are made at the local level, and few local governments have the geologic expertise to interpret geologic maps and glean from them the information on geologic hazards and resources that are of interest to them. California law requires CGS to prepare several products specifically for use in hazard and resource evaluation by local government. Those maps are derivatives of geologic maps and contain only the information needed by land-use planners and decision-makers. This paper briefly describes examples of digital mapping techniques in use at CGS to create maps for an audience that includes geologists, who want all the details of our geologic observations, and for other audiences who want only the information that direc...

Open-File Report, 2011

The U.S. Geological Survey, Multi Hazards Demonstration Project (MHDP) uses hazards science to im... more The U.S. Geological Survey, Multi Hazards Demonstration Project (MHDP) uses hazards science to improve resiliency of communities to natural disasters including earthquakes, tsunamis, wildfires, landslides, floods and coastal erosion. The project engages emergency planners, businesses, universities, government agencies, and others in preparing for major natural disasters. The project also helps to set research goals and provides decision-making information for loss reduction and improved resiliency. The first public product of the MHDP was the ShakeOut Earthquake Scenario published in May 2008. This detailed depiction of a hypothetical magnitude 7.8 earthquake on the San Andreas Fault in southern California served as the centerpiece of the largest earthquake drill in United States history, involving over 5,000 emergency responders and the participation of over 5.5 million citizens. This document summarizes the next major public project for MHDP, a winter storm scenario called ARkStorm (for Atmospheric River 1,000). Experts have designed a large, scientifically realistic meteorological event followed by an examination of the secondary hazards (for example, landslides and flooding), physical damages to the built environment, and social and economic consequences. The hypothetical storm depicted here would strike the U.S. West Coast and be similar to the intense California winter storms of 1861 and 1862 that left the central valley of California impassible. The storm is estimated to produce precipitation that in many places exceeds levels only experienced on average once every 500 to 1,000 years. Extensive flooding results. In many cases flooding overwhelms the state's flood-protection system, which is typically designed to resist 100-to 200-year runoffs. The Central Valley experiences hypothetical flooding 300 miles long and 20 or more miles wide. Serious flooding also occurs in Orange County, Los Angeles County, San Diego, the San Francisco Bay area, and other coastal communities. Windspeeds in some places reach 125 miles per hour, hurricaneforce winds. Across wider areas of the state, winds reach 60 miles per hour. Hundreds of landslides damage roads, highways, and homes. Property damage exceeds 300billion,mostfromflooding.Demandsurge(anincreaseinlaborratesandotherrepaircostsaftermajornaturaldisasters)couldincreasepropertylossesby20percent.Agriculturallossesandothercoststorepairlifelines,dewater(drain)floodedislands,andrepairdamagefromlandslides,bringsthetotaldirectpropertylosstonearly300 billion, most from flooding. Demand surge (an increase in labor rates and other repair costs after major natural disasters) could increase property losses by 20 percent. Agricultural losses and other costs to repair lifelines, dewater (drain) flooded islands, and repair damage from landslides, brings the total direct property loss to nearly 300billion,mostfromflooding.Demandsurge(anincreaseinlaborratesandotherrepaircostsaftermajornaturaldisasters)couldincreasepropertylossesby20percent.Agriculturallossesandothercoststorepairlifelines,dewater(drain)floodedislands,andrepairdamagefromlandslides,bringsthetotaldirectpropertylosstonearly400 billion, of which 20to20 to 20to30 billion would be recoverable through public and commercial insurance. Power, water, sewer, and other lifelines experience damage that takes weeks or months to restore. Flooding evacuation could involve 1.5 million residents in the inland region and delta counties. Business interruption costs reach 325billioninadditiontothe325 billion in addition to the 325billioninadditiontothe400 billion property repair costs, meaning that an ARkStorm could cost on the order of $725 billion, which is nearly 3 times the loss deemed to be realistic by the ShakeOut authors for a severe southern California earthquake, an event with roughly the same annual occurrence probability. K Street, Sacramento, looking east 1861-1862 vi The ARkStorm has several public policy implications: (1) An ARkStorm raises serious questions about the ability of existing federal, state, and local disaster planning to handle a disaster of this magnitude. (2) A core policy issue raised is whether to pay now to mitigate, or pay a lot more later for recovery. (3) Innovative financing solutions are likely to be needed to avoid fiscal crisis and adequately fund response and recovery costs from a similar, real, disaster. (4) Responders and government managers at all levels could be encouraged to conduct risk assessments, and devise the full spectrum of exercises, to exercise ability of their plans to address a similar event. (5) ARkStorm can be a reference point for application of Federal Emergency Management Agency (FEMA) and California Emergency Management Agency guidance connecting federal, state and local natural hazards mapping and mitigation planning under the National Flood Insurance Plan and Disaster Mitigation Act of 2000. (6) Common messages to educate the public about the risk of such an extreme disaster as the ARkStorm scenario could be developed and consistently communicated to facilitate policy formulation and transformation. These impacts were estimated by a team of 117 scientists, engineers, public-policy experts, insurance experts, and employees of the affected lifelines. In many aspects the ARkStorm produced new science, such as the model of coastal inundation. The products of the ARkStorm are intended for use by emergency planners, utility operators, policymakers, and others to inform preparedness plans and to enhance resiliency.

Open-File Report, 2004

Detailed mapping of soil and sediment layers in targeted coastal regions to develop a chronology ... more Detailed mapping of soil and sediment layers in targeted coastal regions to develop a chronology of large prehistoric tsunamis and determine the potential for ground failure and liquefaction • Offshore high-resolution multibeam bathymetric data to locate active faults on the seafloor and identify past landslides • Utilization of marine seismic reflection data, collected by private industry along the west coast in the 1970's and 1980's for oil and gas exploration, to improve our knowledge of the location and subsurface geometry of offshore faults (and hence their earthquake potential). The USGS is currently involved in efforts to rescue these data.

Open-File Report, 2008

through-going events. By combining paleoseismic data into large sets of scenarios and selecting v... more through-going events. By combining paleoseismic data into large sets of scenarios and selecting viable scenarios using external constraints, our method provides rupture histories useful for seismic hazard assessment without having to first settle which event at a site correlates with that at adjoining sites. This should allow paleoseismic data to be used with greater power to understand the seismic hazard posed by faults like the southern San Andreas.

This year, the California Geological Survey will release a new geologic map of the Point Sur 30′ ... more This year, the California Geological Survey will release a new geologic map of the Point Sur 30′ x 60′ quadrangle. Like previous maps in the CGS Regional Geologic Map series, the map will be on a 1:100,000-scale base map, but preserve as much detail as possible from original mapping at larger scale. The area of this map extends about 80 km east-west from the coast at Point Sur to the Bitterwater Valley along the San Andreas Fault Zone. It extends about 55 km north-south from Carmel Highlands to Lucia along the coast, and from Soledad to San Ardo in the Salinas Valley. The Point Sur 30' x 60' quadrangle includes much of the rugged Big Sur coastline, National Forest and wilderness in the Santa Lucia Mountains, and some of the richest farmland in the world in the Salinas Valley. The quadrangle lies entirely within the California Coast Ranges physiographic province and is underlain by two fundamentally different basement terranes of Mesozoic age: the Franciscan Complex and the Salinian block. The Salinian block is a northwardtransported tectonic block of granitic and metamorphic rocks, covered in part by Cretaceous and Cenozoic sedimentary rocks. The map has been compiled from many scientific studies in different parts of the quadrangle, and represents the work of many geologists. The geologic map of the Point Sur 30' x 60' quadrangle builds on compilation by the late Lew Rosenberg for the Monterey County General Plan (Rosenberg, 2001). Lew was working toward a completed geologic map in the format used for CGS regional geologic maps when he became ill in 2010. He passed away in 2013. This map represents an attempt to honor Lew's legacy by completing the map he had so far along. Additional effort has gone into creating a single uniform nomenclature for the geologic units in the map area and incorporating new mapping published in the past few years. The map will be released for review and comments on the CGS web

Landslide-inventory maps are the most basic type of landslide hazard maps; they portray the locat... more Landslide-inventory maps are the most basic type of landslide hazard maps; they portray the location of past landslides and are an indicator of landslide susceptibility. Generally landslide inventories represent a geomorphic interpretation of an area and identification of landforms that may have formed by landsliding. Inventory maps do not necessarily distinguish the age of landslide movements, but given a trigger, some of the mapped slides-or more frequently, portions of them-may become active. The California Geological Survey (CGS) is digitizing existing maps of landslides and has prepared a statewide landslide database that is now available online. The database shows many of the landslides mapped by CGS and others over the past 50 years for the state of California. Individual landslide records reflect the standards of the project for which the landslide was mapped. Many maps show landslide source areas (scarps) separately from landslide deposits while others combine scarps and deposits into a single feature. The information recorded about each landslide has increased over time, so more information is available for more recently mapped landslides. Updates to the database are continuing, both to include more existing maps and to add or update landslides as they occur. The landslide inventory, in combination with the map of susceptibility to deep-seated landslides (CGS Map Sheet 58) can give local planners, infrastructure owners, and the public a perspective on where landslides are most likely to be triggered by winter storms or earthquakes in California. Significant speaker notes are included in the PDF version of the presentation as an annotation layer.

Geotechnical Engineering for Transportation Projects, 2004

We present fault displacement data, regressions, and a methodology to calculate in both a probabi... more We present fault displacement data, regressions, and a methodology to calculate in both a probabilistic and deterministic framework the fault rupture hazard for strike‐slip faults. To assess this hazard we consider: (1) the size of the earthquake and probability that it will rupture to the ...

Natural Hazards Review, 2016

ABSTRACT

Seismological Research Letters, 2004

Earthquake Spectra, 2010

In this paper, we have combined the U.S. Geological Survey's National Seismic Hazard Maps mod... more In this paper, we have combined the U.S. Geological Survey's National Seismic Hazard Maps model with the California geologic map showing 17 generalized geologic units that can be defined by their VS30. We regrouped these units into seven VS30values and calculated a probabilistic seismic hazard map for the entire state for each VS30value. By merging seismic hazard maps based on the seven different VS30values, a suite of seismic hazard maps was computed for 0.2 and 1.0 s spectral ordinates at 2% probability of exceedance (PE) in 50 years. The improved hazards maps explicitly incorporate the site effects and their spatial variability on ground motion estimates. The spectral acceleration (SA) at 1.0 s map of seismic shaking potential for California has now been published as California Geological Survey Map Sheet 48.

Earthquake Spectra, 2013

We update annualized and scenario earthquake loss estimations for California using HAZUS, a loss ... more We update annualized and scenario earthquake loss estimations for California using HAZUS, a loss estimation tool developed by the Federal Emergency Management Agency, and evaluate the effects of changes in input ground motions over the last decade on estimated earthquake losses. Our estimated statewide average earthquake loss to building stock from shaking is approximately $2.8 billion per year, with 32% of it occurring in Los Angeles County and 23% in the San Francisco-Oakland-Fremont metropolitan statistical area. This estimate reflects a 25% to 28% reduction because of changes in input ground motions. Scenario results indicate a 28% to 63% reduction in estimated building economic losses because of changes in input ground motions. Changes in input ground motions are mainly attributed to the use of next generation attenuation relations and, to a lesser extent, to updated earthquake source models and differing approaches for incorporating near-surface site effects.

Bulletin of the Seismological Society of America, 2006

Consideration of site conditions is a vital step in analyzing and predicting earthquake ground mo... more Consideration of site conditions is a vital step in analyzing and predicting earthquake ground motion. The importance of amplification by soil conditions has long been recognized, but though many seismic-instrument sites have been characterized by their geologic conditions, there has been no consistent, simple classification applied to all sites. As classification of sites by shear-wave velocity has become more common, the need to go back and provide a simple uniform classification for all stations has become apparent. Within the Pacific Earthquake Engineering Research Center's Next Generation Attenuation equation project, developers of attenuation equations recognized the need to consider site conditions and asked that the California Geological Survey provide site conditions information for all stations that have recorded earthquake ground motion in California. To provide these estimates, we sorted the available shear-wave velocity data by geologic unit, generalized the geologic units, and prepared a map so that we could use the extent of the map units to transfer the velocity characteristics from the sites where they were measured to sites on the same or similar materials. This new map is different from the California Geological Survey "preliminary site-conditions map of California" in that 19 geologically defined categories are used, rather than National Earthquake Hazards Reduction Program categories. Although this map does not yet cover all of California, when completed it may provide a basis for more precise consideration of site conditions in ground-motion calculations.

Geological Society of America Abstracts with Programs, 2016

Earthquake Spectra, 2010

A statistical evaluation of shaking damage to wood-framed houses caused by the 2003 M6.5 San Sime... more A statistical evaluation of shaking damage to wood-framed houses caused by the 2003 M6.5 San Simeon earthquake indicates that both the rate and severity of damage, independent of structure type, are significantly greater on hilltops compared to hill slopes when underlain by Cretaceous or Tertiary sedimentary rocks. This increase in damage is interpreted to be the result of topographic amplification. An increase in the damage rate is found for all structures built on Plio-Pleistocene rocks independent of topographic position, and this is interpreted to be the result of amplified shaking caused by geologic site response. Damage rate and severity to houses built on Tertiary rocks suggest that amplification due to both topographic position and geologic site response may be occurring in these rocks, but effects from other topographic parameters cannot be ruled out. For all geologic and topographic conditions, houses with raised foundations are more frequently damaged than those with slab...

The California Geological Survey (CGS) uses digital mapping techniques to prepare products for a ... more The California Geological Survey (CGS) uses digital mapping techniques to prepare products for a wide variety of users, who range from geologists to engineers to local government planners and the public. In California, almost all land-use planning and building decisions are made at the local level, and few local governments have the geologic expertise to interpret geologic maps and glean from them the information on geologic hazards and resources that are of interest to them. California law requires CGS to prepare several products specifically for use in hazard and resource evaluation by local government. Those maps are derivatives of geologic maps and contain only the information needed by land-use planners and decision-makers. This paper briefly describes examples of digital mapping techniques in use at CGS to create maps for an audience that includes geologists, who want all the details of our geologic observations, and for other audiences who want only the information that direc...

Open-File Report, 2011

The U.S. Geological Survey, Multi Hazards Demonstration Project (MHDP) uses hazards science to im... more The U.S. Geological Survey, Multi Hazards Demonstration Project (MHDP) uses hazards science to improve resiliency of communities to natural disasters including earthquakes, tsunamis, wildfires, landslides, floods and coastal erosion. The project engages emergency planners, businesses, universities, government agencies, and others in preparing for major natural disasters. The project also helps to set research goals and provides decision-making information for loss reduction and improved resiliency. The first public product of the MHDP was the ShakeOut Earthquake Scenario published in May 2008. This detailed depiction of a hypothetical magnitude 7.8 earthquake on the San Andreas Fault in southern California served as the centerpiece of the largest earthquake drill in United States history, involving over 5,000 emergency responders and the participation of over 5.5 million citizens. This document summarizes the next major public project for MHDP, a winter storm scenario called ARkStorm (for Atmospheric River 1,000). Experts have designed a large, scientifically realistic meteorological event followed by an examination of the secondary hazards (for example, landslides and flooding), physical damages to the built environment, and social and economic consequences. The hypothetical storm depicted here would strike the U.S. West Coast and be similar to the intense California winter storms of 1861 and 1862 that left the central valley of California impassible. The storm is estimated to produce precipitation that in many places exceeds levels only experienced on average once every 500 to 1,000 years. Extensive flooding results. In many cases flooding overwhelms the state's flood-protection system, which is typically designed to resist 100-to 200-year runoffs. The Central Valley experiences hypothetical flooding 300 miles long and 20 or more miles wide. Serious flooding also occurs in Orange County, Los Angeles County, San Diego, the San Francisco Bay area, and other coastal communities. Windspeeds in some places reach 125 miles per hour, hurricaneforce winds. Across wider areas of the state, winds reach 60 miles per hour. Hundreds of landslides damage roads, highways, and homes. Property damage exceeds 300billion,mostfromflooding.Demandsurge(anincreaseinlaborratesandotherrepaircostsaftermajornaturaldisasters)couldincreasepropertylossesby20percent.Agriculturallossesandothercoststorepairlifelines,dewater(drain)floodedislands,andrepairdamagefromlandslides,bringsthetotaldirectpropertylosstonearly300 billion, most from flooding. Demand surge (an increase in labor rates and other repair costs after major natural disasters) could increase property losses by 20 percent. Agricultural losses and other costs to repair lifelines, dewater (drain) flooded islands, and repair damage from landslides, brings the total direct property loss to nearly 300billion,mostfromflooding.Demandsurge(anincreaseinlaborratesandotherrepaircostsaftermajornaturaldisasters)couldincreasepropertylossesby20percent.Agriculturallossesandothercoststorepairlifelines,dewater(drain)floodedislands,andrepairdamagefromlandslides,bringsthetotaldirectpropertylosstonearly400 billion, of which 20to20 to 20to30 billion would be recoverable through public and commercial insurance. Power, water, sewer, and other lifelines experience damage that takes weeks or months to restore. Flooding evacuation could involve 1.5 million residents in the inland region and delta counties. Business interruption costs reach 325billioninadditiontothe325 billion in addition to the 325billioninadditiontothe400 billion property repair costs, meaning that an ARkStorm could cost on the order of $725 billion, which is nearly 3 times the loss deemed to be realistic by the ShakeOut authors for a severe southern California earthquake, an event with roughly the same annual occurrence probability. K Street, Sacramento, looking east 1861-1862 vi The ARkStorm has several public policy implications: (1) An ARkStorm raises serious questions about the ability of existing federal, state, and local disaster planning to handle a disaster of this magnitude. (2) A core policy issue raised is whether to pay now to mitigate, or pay a lot more later for recovery. (3) Innovative financing solutions are likely to be needed to avoid fiscal crisis and adequately fund response and recovery costs from a similar, real, disaster. (4) Responders and government managers at all levels could be encouraged to conduct risk assessments, and devise the full spectrum of exercises, to exercise ability of their plans to address a similar event. (5) ARkStorm can be a reference point for application of Federal Emergency Management Agency (FEMA) and California Emergency Management Agency guidance connecting federal, state and local natural hazards mapping and mitigation planning under the National Flood Insurance Plan and Disaster Mitigation Act of 2000. (6) Common messages to educate the public about the risk of such an extreme disaster as the ARkStorm scenario could be developed and consistently communicated to facilitate policy formulation and transformation. These impacts were estimated by a team of 117 scientists, engineers, public-policy experts, insurance experts, and employees of the affected lifelines. In many aspects the ARkStorm produced new science, such as the model of coastal inundation. The products of the ARkStorm are intended for use by emergency planners, utility operators, policymakers, and others to inform preparedness plans and to enhance resiliency.

Open-File Report, 2004

Detailed mapping of soil and sediment layers in targeted coastal regions to develop a chronology ... more Detailed mapping of soil and sediment layers in targeted coastal regions to develop a chronology of large prehistoric tsunamis and determine the potential for ground failure and liquefaction • Offshore high-resolution multibeam bathymetric data to locate active faults on the seafloor and identify past landslides • Utilization of marine seismic reflection data, collected by private industry along the west coast in the 1970's and 1980's for oil and gas exploration, to improve our knowledge of the location and subsurface geometry of offshore faults (and hence their earthquake potential). The USGS is currently involved in efforts to rescue these data.

Open-File Report, 2008

through-going events. By combining paleoseismic data into large sets of scenarios and selecting v... more through-going events. By combining paleoseismic data into large sets of scenarios and selecting viable scenarios using external constraints, our method provides rupture histories useful for seismic hazard assessment without having to first settle which event at a site correlates with that at adjoining sites. This should allow paleoseismic data to be used with greater power to understand the seismic hazard posed by faults like the southern San Andreas.

This year, the California Geological Survey will release a new geologic map of the Point Sur 30′ ... more This year, the California Geological Survey will release a new geologic map of the Point Sur 30′ x 60′ quadrangle. Like previous maps in the CGS Regional Geologic Map series, the map will be on a 1:100,000-scale base map, but preserve as much detail as possible from original mapping at larger scale. The area of this map extends about 80 km east-west from the coast at Point Sur to the Bitterwater Valley along the San Andreas Fault Zone. It extends about 55 km north-south from Carmel Highlands to Lucia along the coast, and from Soledad to San Ardo in the Salinas Valley. The Point Sur 30' x 60' quadrangle includes much of the rugged Big Sur coastline, National Forest and wilderness in the Santa Lucia Mountains, and some of the richest farmland in the world in the Salinas Valley. The quadrangle lies entirely within the California Coast Ranges physiographic province and is underlain by two fundamentally different basement terranes of Mesozoic age: the Franciscan Complex and the Salinian block. The Salinian block is a northwardtransported tectonic block of granitic and metamorphic rocks, covered in part by Cretaceous and Cenozoic sedimentary rocks. The map has been compiled from many scientific studies in different parts of the quadrangle, and represents the work of many geologists. The geologic map of the Point Sur 30' x 60' quadrangle builds on compilation by the late Lew Rosenberg for the Monterey County General Plan (Rosenberg, 2001). Lew was working toward a completed geologic map in the format used for CGS regional geologic maps when he became ill in 2010. He passed away in 2013. This map represents an attempt to honor Lew's legacy by completing the map he had so far along. Additional effort has gone into creating a single uniform nomenclature for the geologic units in the map area and incorporating new mapping published in the past few years. The map will be released for review and comments on the CGS web

Landslide-inventory maps are the most basic type of landslide hazard maps; they portray the locat... more Landslide-inventory maps are the most basic type of landslide hazard maps; they portray the location of past landslides and are an indicator of landslide susceptibility. Generally landslide inventories represent a geomorphic interpretation of an area and identification of landforms that may have formed by landsliding. Inventory maps do not necessarily distinguish the age of landslide movements, but given a trigger, some of the mapped slides-or more frequently, portions of them-may become active. The California Geological Survey (CGS) is digitizing existing maps of landslides and has prepared a statewide landslide database that is now available online. The database shows many of the landslides mapped by CGS and others over the past 50 years for the state of California. Individual landslide records reflect the standards of the project for which the landslide was mapped. Many maps show landslide source areas (scarps) separately from landslide deposits while others combine scarps and deposits into a single feature. The information recorded about each landslide has increased over time, so more information is available for more recently mapped landslides. Updates to the database are continuing, both to include more existing maps and to add or update landslides as they occur. The landslide inventory, in combination with the map of susceptibility to deep-seated landslides (CGS Map Sheet 58) can give local planners, infrastructure owners, and the public a perspective on where landslides are most likely to be triggered by winter storms or earthquakes in California. Significant speaker notes are included in the PDF version of the presentation as an annotation layer.

Geotechnical Engineering for Transportation Projects, 2004

We present fault displacement data, regressions, and a methodology to calculate in both a probabi... more We present fault displacement data, regressions, and a methodology to calculate in both a probabilistic and deterministic framework the fault rupture hazard for strike‐slip faults. To assess this hazard we consider: (1) the size of the earthquake and probability that it will rupture to the ...

Natural Hazards Review, 2016

ABSTRACT

Seismological Research Letters, 2004

Earthquake Spectra, 2010

In this paper, we have combined the U.S. Geological Survey's National Seismic Hazard Maps mod... more In this paper, we have combined the U.S. Geological Survey's National Seismic Hazard Maps model with the California geologic map showing 17 generalized geologic units that can be defined by their VS30. We regrouped these units into seven VS30values and calculated a probabilistic seismic hazard map for the entire state for each VS30value. By merging seismic hazard maps based on the seven different VS30values, a suite of seismic hazard maps was computed for 0.2 and 1.0 s spectral ordinates at 2% probability of exceedance (PE) in 50 years. The improved hazards maps explicitly incorporate the site effects and their spatial variability on ground motion estimates. The spectral acceleration (SA) at 1.0 s map of seismic shaking potential for California has now been published as California Geological Survey Map Sheet 48.

Earthquake Spectra, 2013

We update annualized and scenario earthquake loss estimations for California using HAZUS, a loss ... more We update annualized and scenario earthquake loss estimations for California using HAZUS, a loss estimation tool developed by the Federal Emergency Management Agency, and evaluate the effects of changes in input ground motions over the last decade on estimated earthquake losses. Our estimated statewide average earthquake loss to building stock from shaking is approximately $2.8 billion per year, with 32% of it occurring in Los Angeles County and 23% in the San Francisco-Oakland-Fremont metropolitan statistical area. This estimate reflects a 25% to 28% reduction because of changes in input ground motions. Scenario results indicate a 28% to 63% reduction in estimated building economic losses because of changes in input ground motions. Changes in input ground motions are mainly attributed to the use of next generation attenuation relations and, to a lesser extent, to updated earthquake source models and differing approaches for incorporating near-surface site effects.

Bulletin of the Seismological Society of America, 2006

Consideration of site conditions is a vital step in analyzing and predicting earthquake ground mo... more Consideration of site conditions is a vital step in analyzing and predicting earthquake ground motion. The importance of amplification by soil conditions has long been recognized, but though many seismic-instrument sites have been characterized by their geologic conditions, there has been no consistent, simple classification applied to all sites. As classification of sites by shear-wave velocity has become more common, the need to go back and provide a simple uniform classification for all stations has become apparent. Within the Pacific Earthquake Engineering Research Center's Next Generation Attenuation equation project, developers of attenuation equations recognized the need to consider site conditions and asked that the California Geological Survey provide site conditions information for all stations that have recorded earthquake ground motion in California. To provide these estimates, we sorted the available shear-wave velocity data by geologic unit, generalized the geologic units, and prepared a map so that we could use the extent of the map units to transfer the velocity characteristics from the sites where they were measured to sites on the same or similar materials. This new map is different from the California Geological Survey "preliminary site-conditions map of California" in that 19 geologically defined categories are used, rather than National Earthquake Hazards Reduction Program categories. Although this map does not yet cover all of California, when completed it may provide a basis for more precise consideration of site conditions in ground-motion calculations.

Geological Society of America Abstracts with Programs, 2016