Geology topics

Arthur D. Frankel

Publications and source records attributed to Arthur D. Frankel.

At least 55 records · Page 3Linked to original sources

USGS2018

Effects of simulated magnitude 9 earthquake motions on structures in the Pacific Northwest

The Cascadia Subduction Zone (CSZ) produces long-duration, large-magnitude earthquakes that could severely affect structures in the Pacific Northwest (PNW). The impact of synthetic M9.0 CSZ earthquakes on buildings in the Pacific Northwest is studied using eight reinforced concrete wall archetypes that range from 4 to 40 stories. These archetypes were subjected to an ensemble of simulated ground-motions from 30 M9 earthquakes for a location in Seattle that overlies a ~8km deep sedimentary basin and an equivalent location outside the basin. Long-period (1-7s) ground motions are strongly amplified in the CSZ synthetics within the Seattle Basin, leading to a 6-fold increase in deformation demand (inter-story drift) compared to an equivalent out of basin site. The variability in demand was also found to be much larger inside the basin than outside the basin.

Conference Paper↗

USGS2017

Effects of deep basins on structural collapse during large subduction earthquakes

Deep sedimentary basins are known to increase the intensity of ground motions, but this effect is implicitly considered in seismic hazard maps used in U.S. building codes. The basin amplification of ground motions from subduction earthquakes is particularly important in the Pacific Northwest, where the hazard at long periods is dominated by such earthquakes. This paper evaluates the effects of basins on spectral accelerations, ground-motion duration, spectral shape, and structural collapse using subduction earthquake recordings from basins in Japan that have similar depths as the Puget Lowland basin. For three of the Japanese basins and the Puget Lowland basin, the spectral accelerations were amplified by a factor of 2 to 4 for periods above 2.0 s. The long-duration subduction earthquakes and the effects of basins on spectral shape combined, lower the spectral accelerations at collapse for a set of building archetypes relative to other ground motions. For the hypothetical case in which these motions represent the entire hazard, the archetypes would need to increase up to 3.3 times its strength to compensate for these effects.

Earthquake Spectra↗

USGS2017

Evaluating a kinematic method for generating broadband ground motions for great subduction zone earthquakes: Application to the 2003 Mw 8.3 Tokachi‐Oki earthquake

We compare broadband synthetic seismograms with recordings of the 2003 M w "> M w Mw 8.3 Tokachi‐Oki earthquake to evaluate a compound rupture model, in which slip on the fault consists of multiple high‐stress‐drop asperities superimposed on a background slip distribution with longer rise times. Low‐frequency synthetics ( < 1    Hz "> < 1 Hz <1 Hz ) are calculated using deterministic, 3D finite‐difference simulations and are combined with high‐frequency ( > 1    Hz "> > 1 Hz >1 Hz ) stochastic synthetics using a matched filter at 1 Hz. We show that this compound rupture model and overall approach accurately reproduces waveform envelopes and observed response spectral accelerations (SAs) from the Tokachi‐Oki event. We find that sufficiently short subfault rise times (i.e., < ∼ 1 – 2    s "> < ∼ 1 – 2 s <∼1–2 s ) are necessary to reproduce energy ∼ 1    Hz "> ∼ 1 Hz ∼1 Hz . This is achieved by either (1) including distinct subevents with short rise times, as may be suggested by the Tokachi‐Oki data, or (2) imposing a fast‐slip velocity over the entire rupture area. We also include a systematic study on the effects of varying several kinematic rupture parameters. We find that simulated strong ground motions are sensitive to the average rupture velocity and coherence of the rupture front, with more coherent ruptures yielding higher response SAs. We also assess the effects of varying the average slip velocity and the character (i.e., area, magnitude, and location) of high‐stress‐drop subevents. Even in the absence of precise constraints on these kinematic rupture parameters, our simulations still reproduce major features in the Tokachi‐Oki earthquake data, supporting its accuracy in modeling future large earthquakes.

Bulletin of the Seismological Society of America↗

USGS2017

3D ground‐motion simulations of Mw 7 earthquakes on the Salt Lake City segment of the Wasatch fault zone: Variability of long‐period (T≥1 s) ground motions and sensitivity to kinematic rupture parameters

We examine the variability of long‐period ( T ≥1 s) earthquake ground motions from 3D simulations of M w 7 earthquakes on the Salt Lake City segment of the Wasatch fault zone, Utah, from a set of 96 rupture models with varying slip distributions, rupture speeds, slip velocities, and hypocenter locations. Earthquake ruptures were prescribed on a 3D fault representation that satisfies geologic constraints and maintained distinct strands for the Warm Springs and for the East Bench and Cottonwood faults. Response spectral accelerations (SA; 1.5–10 s; 5% damping) were measured, and average distance scaling was well fit by a simple functional form that depends on the near‐source intensity level SA 0 ( T ) and a corner distance R c :SA( R , T )=SA 0 ( T )(1+( R / R c )) −1 . Period‐dependent hanging‐wall effects manifested and increased the ground motions by factors of about 2–3, though the effects appeared partially attributable to differences in shallow site response for sites on the hanging wall and footwall of the fault. Comparisons with modern ground‐motion prediction equations (GMPEs) found that the simulated ground motions were generally consistent, except within deep sedimentary basins, where simulated ground motions were greatly underpredicted. Ground‐motion variability exhibited strong lateral variations and, at some sites, exceeded the ground‐motion variability indicated by GMPEs. The effects on the ground motions of changing the values of the five kinematic rupture parameters can largely be explained by three predominant factors: distance to high‐slip subevents, dynamic stress drop, and changes in the contributions from directivity. These results emphasize the need for further characterization of the underlying distributions and covariances of the kinematic rupture parameters used in 3D ground‐motion simulations employed in probabilistic seismic‐hazard analyses.

Utah↗

USGS2017

Reducing risk where tectonic plates collide—U.S. Geological Survey subduction zone science plan

The U.S. Geological Survey (USGS) serves the Nation by providing reliable scientific information and tools to build resilience in communities exposed to subduction zone earthquakes, tsunamis, landslides, and volcanic eruptions. Improving the application of USGS science to successfully reduce risk from these events relies on whole community efforts, with continuing partnerships among scientists and stakeholders, including researchers from universities, other government labs and private industry, land-use planners, engineers, policy-makers, emergency managers and responders, business owners, insurance providers, the media, and the general public. Motivated by recent technological advances and increased awareness of our growing vulnerability to subduction-zone hazards, the USGS is uniquely positioned to take a major step forward in the science it conducts and products it provides, building on its tradition of using long-term monitoring and research to develop effective products for hazard mitigation. This science plan provides a blueprint both for prioritizing USGS science activities and for delineating USGS interests and potential participation in subduction zone science supported by its partners. The activities in this plan address many USGS stakeholder needs: High-fidelity tools and user-tailored information that facilitate increasingly more targeted, neighborhood-scale decisions to mitigate risks more cost-effectively and ensure post-event operability. Such tools may include maps, tables, and simulated earthquake ground-motion records conveying shaking intensity and frequency. These facilitate the prioritization of retrofitting of vulnerable infrastructure; Information to guide local land-use and response planning to minimize development in likely hazardous zones (for example, databases, maps, and scenario documents to guide evacuation route planning in communities near volcanoes, along coastlines vulnerable to tsunamis, and built on landslide-prone terrain); New tools to assess the potential for cascading hazards, such as landslides, tsunamis, coastal changes, and flooding caused by earthquakes or volcanic eruptions; Geospatial models of permanent, widespread land- and sea-level changes that may occur in the immediate aftermath of great ( M ≥8.0) subduction zone earthquakes; Strong partnerships between scientists and public safety providers for effective decision making during periods of elevated hazard and risk; Accurate forecasts of far-reaching hazards (for example, ash clouds, tsunamis) to avert catastrophes and unnecessary disruptions in air and sea transportation; Aftershock forecasts to guide decisions about when and where to re-enter, repair, or rebuild buildings and infrastructure, for all types of subduction zone earthquakes.

Circular↗

USGS2017

3-D simulations of M9 earthquakes on the Cascadia Megathrust: Key parameters and uncertainty

Geologic and historical records indicate that the Cascadia subduction zone is capable of generating large, megathrust earthquakes up to magnitude 9. The last great Cascadia earthquake occurred in 1700, and thus there is no direct measure on the intensity of ground shaking or specific rupture parameters from seismic recordings. We use 3-D numerical simulations to generate broadband (0-10 Hz) synthetic seismograms for 50 M9 rupture scenarios on the Cascadia megathrust. Slip consists of multiple high-stress drop subevents (~M8) with short rise times on the deeper portion of the fault, superimposed on a background slip distribution with longer rise times. We find a >4x variation in the intensity of ground shaking depending upon several key parameters, including the down-dip limit of rupture, the slip distribution and location of strong-motion-generating subevents, and the hypocenter location. We find that extending the down-dip limit of rupture to the top of the non-volcanic tremor zone results in a ~2-3x increase in peak ground acceleration for the inland city of Seattle, Washington, compared to a completely offshore rupture. However, our simulations show that allowing the rupture to extend to the up-dip limit of tremor (i.e., the deepest rupture extent in the National Seismic Hazard Maps), even when tapering the slip to zero at the down-dip edge, results in multiple areas of coseismic coastal uplift. This is inconsistent with coastal geologic evidence (e.g., buried soils, submerged forests), which suggests predominantly coastal subsidence for the 1700 earthquake and previous events. Defining the down-dip limit of rupture as the 1 cm/yr locking contour (i.e., mostly offshore) results in primarily coseismic subsidence at coastal sites. We also find that the presence of deep subevents can produce along-strike variations in subsidence and ground shaking along the coast. Our results demonstrate the wide range of possible ground motions from an M9 megathrust earthquake in Cascadia, and the potential to further constrain key rupture parameters using geologic and geophysical observations, ultimately improving our estimation of seismic hazard associated with the Cascadia megathrust.

Conference Paper↗

USGS2016

Modeling strong‐motion recordings of the 2010 Mw 8.8 Maule, Chile, earthquake with high stress‐drop subevents and background slip

Strong‐motion recordings of the M w 8.8 Maule earthquake were modeled using a compound rupture model consisting of (1) a background slip distribution with large correlation lengths, relatively low slip velocity, and long peak rise time of slip of about 10 s and (2) high stress‐drop subevents (asperities) on the deeper portion of the rupture with moment magnitudes 7.9–8.2, high slip velocity, and rise times of slip of about 2 s. In this model, the high‐frequency energy is not produced in the same location as the peak coseismic slip, but is generated in the deeper part of the rupture zone. Using synthetic seismograms generated for a plane‐layered velocity model, I find that the high stress‐drop subevents explain the observed Fourier spectral amplitude from about 0.1 to 1.0 Hz. Broadband synthetics (0–10 Hz) were calculated by combining deterministic synthetics derived from the background slip and asperities (≤1 Hz) with stochastic synthetics generated only at the asperities (≥1 Hz). The broadband synthetics produced response spectral accelerations with low bias compared to the data, for periods of 0.1–10 s. A subevent stress drop of 200–350 bars for the high‐frequency stochastic synthetics was found to bracket the observed spectral accelerations at frequencies greater than 1 Hz. For most of the stations, the synthetics had durations of the Arias intensity similar to the observed records.

Maule↗

USGS2016

Building a subduction zone observatory

Subduction zones contain many of Earth’s most remarkable geologic structures, from the deepest oceanic trenches to glacier-covered mountains and steaming volcanoes. These environments formed through spectacular events: Nature’s largest earthquakes, tsunamis, and volcanic eruptions are born here.

Eos, Earth and Space Science News↗

USGS2015

Seismic source characterization for the 2014 update of the U.S. National Seismic Hazard Model

We present the updated seismic source characterization (SSC) for the 2014 update of the National Seismic Hazard Model (NSHM) for the conterminous United States. Construction of the seismic source models employs the methodology that was developed for the 1996 NSHM but includes new and updated data, data types, source models, and source parameters that reflect the current state of knowledge of earthquake occurrence and state of practice for seismic hazard analyses. We review the SSC parameterization and describe the methods used to estimate earthquake rates, magnitudes, locations, and geometries for all seismic source models, with an emphasis on new source model components. We highlight the effects that two new model components—incorporation of slip rates from combined geodetic-geologic inversions and the incorporation of adaptively smoothed seismicity models—have on probabilistic ground motions, because these sources span multiple regions of the conterminous United States and provide important additional epistemic uncertainty for the 2014 NSHM.

Earthquake Spectra↗

USGS2015

2014 Update of the Pacific Northwest portion of the U.S. National Seismic Hazard Maps

Several aspects of the earthquake characterization were changed for the Pacific Northwest portion of the 2014 update of the national seismic hazard maps, reflecting recent scientific findings. New logic trees were developed for the recurrence parameters of M8-9 earthquakes on the Cascadia subduction zone (CSZ) and for the eastern edge of their rupture zones. These logic trees reflect recent findings of additional M8 CSZ earthquakes using offshore deposits of turbidity flows and onshore tsunami deposits and subsidence. These M8 earthquakes each rupture a portion of the CSZ and occur in the time periods between M9 earthquakes that have an average recurrence interval of about 500 years. The maximum magnitude was increased for deep intraslab earthquakes. An areal source zone to account for the possibility of deep earthquakes under western Oregon was expanded. The western portion of the Tacoma fault was added to the hazard maps.

Earthquake Spectra↗

USGS2015

The 2014 United States National Seismic Hazard Model

New seismic hazard maps have been developed for the conterminous United States using the latest data, models, and methods available for assessing earthquake hazard. The hazard models incorporate new information on earthquake rupture behavior observed in recent earthquakes; fault studies that use both geologic and geodetic strain rate data; earthquake catalogs through 2012 that include new assessments of locations and magnitudes; earthquake adaptive smoothing models that more fully account for the spatial clustering of earthquakes; and 22 ground motion models, some of which consider more than double the shaking data applied previously. Alternative input models account for larger earthquakes, more complicated ruptures, and more varied ground shaking estimates than assumed in earlier models. The ground motions, for levels applied in building codes, differ from the previous version by less than ±10% over 60% of the country, but can differ by ±50% in localized areas. The models are incorporated in insurance rates, risk assessments, and as input into the U.S. building code provisions for earthquake ground shaking.

Earthquake Spectra↗

USGS2015

Earthquake forewarning in the Cascadia region

This report, prepared for the National Earthquake Prediction Evaluation Council (NEPEC), is intended as a step toward improving communications about earthquake hazards between information providers and users who coordinate emergency-response activities in the Cascadia region of the Pacific Northwest. NEPEC charged a subcommittee of scientists with writing this report about forewarnings of increased probabilities of a damaging earthquake. We begin by clarifying some terminology; a “prediction” refers to a deterministic statement that a particular future earthquake will or will not occur. In contrast to the 0- or 100-percent likelihood of a deterministic prediction, a “forecast” describes the probability of an earthquake occurring, which may range from >0 to <100 percent. When the time window is short (days to months) and the forecast is formulated for operational utility, this term may be “operational earthquake forecasting.” The subcommittee considered short-term forecasts only, herein referred to as “forewarnings,” but not their formulation into messages or their applications, which will be addressed by NEPEC in subsequent activities. The subcommittee considered “direct” and “indirect” forewarnings. Direct forewarnings originate with observed changes in geologic processes or conditions, which may include Increased rates of M >4 earthquakes on the plate interface north of the Mendocino region Changes in shallow seismicity patterns Increased rates of moderate earthquakes within the subducting plate Changes in the pattern of slow slip on the plate interface and other major faults Indirect forewarnings are based largely on model predictions of increased earthquake-occurrence probabilities. In this context, “models” refers to simulations of the processes believed to affect earthquake occurrence, as implemented in computer software, laboratory experiments, or some analog natural system. These indirect forewarnings likely will be more uncertain and difficult to interpret than direct forewarnings. This report also highlights the challenges of assessing the significance of forewarnings, which mostly will be extraordinary events with little or no historical precedent in the Cascadia region.

Cascadia region↗

USGS2015

Decay of S‐wave amplitudes with distance for earthquakes in the Charlevoix, Quebec, area: Effects of radiation pattern and directivity

The decay of the Fourier spectral amplitudes of S waves over distances of 10–80 km near Charlevoix, Quebec, was determined using waveforms from seven earthquakes with M N 3.3–5.4. The S ‐wave spectral amplitudes were corrected for site response and source amplitude by normalizing the coda‐wave spectrum at a fixed time after the origin time. The amplitude decay with distance was found to be less steep as the frequency increases from 1 to 14, contrary to what would be expected from anelastic and scattering attenuation for a point source with an isotropic radiation pattern. The decay at 14 Hz indicates that the geometrical spreading at distances less than 80 km is less steep than R −1.05 . The steeper distance decay of the low‐frequency spectrum appears to be an artifact of the radiation pattern and rupture directivity, which affect the low‐frequency amplitude more than the high frequency. Synthetic seismograms were made for a horizontally layered crust for the M w 4.6 Rivière du Loup earthquake and an M w 3.3 event. The decay with distance of the 1 Hz spectral amplitudes of the synthetics is similar to that observed for the Rivière du Loup earthquake, indicating that radiation pattern and rupture directivity are important factors in determining the attenuation with distance at 1 Hz. For the M w 3.3 earthquake, the distance decay of the 1 Hz spectral amplitudes was found to be sensitive to the focal mechanism. This study demonstrates that estimates of geometrical spreading made using 1 Hz amplitudes can be contaminated by radiation pattern and directivity effects and may not be applicable for constructing ground‐motion prediction equations for sources with other focal mechanisms and rupture behavior.

Bulletin of the Seismological Society of America↗

USGS2015

Seismic-hazard maps for the conterminous United States, 2014

The maps presented here provide an update to the 2008 data contained in U.S Geological Survey Scientific Investigations Map 3195 ( http://pubs.usgs.gov/sim/3195/ ).Probabilistic seismic-hazard maps were prepared for the conterminous United States for 2014 portraying peak horizontal acceleration and horizontal spectral response acceleration for 0.2- and 1.0-second periods with probabilities of exceedance of 10 percent in 50 years and 2 percent in 50 years. All of the maps were prepared by combining the hazard derived from spatially smoothed historical seismicity with the hazard from fault-specific sources. The acceleration values contoured are the random horizontal component. The reference site condition is firm rock, defined as having an average shear-wave velocity of 760 m/s in the top 30 meters corresponding to the boundary between NEHRP (National Earthquake Hazards Reduction program) site classes B and C. This data set represents the results of calculations of hazard curves for a grid of points with a spacing of 0.05 degrees in latitude and longitude. The grid of points was contoured to produce the final representation of the seismic hazard. These maps are intended to summarize the available quantitative information about seismic ground motion hazard for the conterminous United States from geologic and geophysical sources.

Scientific Investigations Map↗

USGS2014

Implementation of NGA-West2 ground motion models in the 2014 U.S. National Seismic Hazard Maps

The U.S. National Seismic Hazard Maps (NSHMs) have been an important component of seismic design regulations in the United States for the past several decades. These maps present earthquake ground shaking intensities at specified probabilities of being exceeded over a 50-year time period. The previous version of the NSHMs was developed in 2008; during 2012 and 2013, scientists at the U.S. Geological Survey have been updating the maps based on their assessment of the “best available science,” resulting in the 2014 NSHMs. The update includes modifications to the seismic source models and the ground motion models (GMMs) for sites across the conterminous United States. This paper focuses on updates in the Western United States (WUS) due to the use of new GMMs for shallow crustal earthquakes in active tectonic regions developed by the Next Generation Attenuation (NGA-West2) project. Individual GMMs, their weighted combination, and their impact on the hazard maps relative to 2008 are discussed. In general, the combined effects of lower medians and increased standard deviations in the new GMMs have caused only small changes, within 5–20%, in the probabilistic ground motions for most sites across the WUS compared to the 2008 NSHMs.

Earthquake Spectra↗

USGS2014

Modeling the effects of source and path heterogeneity on ground motions of great earthquakes on the Cascadia Subduction Zone Using 3D simulations

We ran finite‐difference earthquake simulations for great subduction zone earthquakes in Cascadia to model the effects of source and path heterogeneity for the purpose of improving strong‐motion predictions. We developed a rupture model for large subduction zone earthquakes based on a k −2 slip spectrum and scale‐dependent rise times by representing the slip distribution as the sum of normal modes of a vibrating membrane. Finite source and path effects were important in determining the distribution of strong motions through the locations of the hypocenter, subevents, and crustal structures like sedimentary basins. Some regions in Cascadia appear to be at greater risk than others during an event due to the geometry of the Cascadia fault zone relative to the coast and populated regions. The southern Oregon coast appears to have increased risk because it is closer to the locked zone of the Cascadia fault than other coastal areas and is also in the path of directivity amplification from any rupture propagating north to south in that part of the subduction zone, and the basins in the Puget Sound area are efficiently amplified by both north and south propagating ruptures off the coast of western Washington. We find that the median spectral accelerations at 5 s period from the simulations are similar to that of the Zhao et al. (2006) ground‐motion prediction equation, although our simulations predict higher amplitudes near the region of greatest slip and in the sedimentary basins, such as the Seattle basin.

Bulletin of the Seismological Society of America↗

USGS2014

Documentation for the 2014 update of the United States national seismic hazard maps

The national seismic hazard maps for the conterminous United States have been updated to account for new methods, models, and data that have been obtained since the 2008 maps were released (Petersen and others, 2008). The input models are improved from those implemented in 2008 by using new ground motion models that have incorporated about twice as many earthquake strong ground shaking data and by incorporating many additional scientific studies that indicate broader ranges of earthquake source and ground motion models. These time-independent maps are shown for 2-percent and 10-percent probability of exceedance in 50 years for peak horizontal ground acceleration as well as 5-hertz and 1-hertz spectral accelerations with 5-percent damping on a uniform firm rock site condition (760 meters per second shear wave velocity in the upper 30 m, V S30 ). In this report, the 2014 updated maps are compared with the 2008 version of the maps and indicate changes of plus or minus 20 percent over wide areas, with larger changes locally, caused by the modifications to the seismic source and ground motion inputs.

Open-File Report↗

USGS2014

Report on workshop to incorporate basin response in the design of tall buildings in the Puget Sound region, Washington

On March 4, 2013, the City of Seattle and the U.S. Geological Survey (USGS) convened a workshop of 25 engineers and seismologists to provide recommendations to the City for the incorporation of amplification of earthquake ground shaking by the Seattle sedimentary basin in the design of tall buildings in Seattle. The workshop was initiated and organized by Susan Chang, a geotechnical engineer with the City of Seattle Department of Planning and Development, along with Art Frankel and Craig Weaver of the USGS. C.B. Crouse of URS Corporation, Seattle made key suggestions for the agenda. The USGS provided travel support for most of the out-of-town participants. The agenda and invited attendees are given in the appendix. The attendees included geotechnical and structural engineers working in Seattle, engineers with experience utilizing basin response factors in other regions, and seismologists who have studied basin response in a variety of locations. In this report, we summarize the technical presentations and the recommendations from the workshop.

Washington↗