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Arthur D. Frankel

Publications and source records attributed to Arthur D. Frankel.

At least 37 records · Page 2Linked to original sources
USGS2021

Expected warning times from the ShakeAlert earthquake early warning system for earthquakes in the Pacific Northwest

The ShakeAlert® earthquake early warning system has been live since October 2019 for the testing of public alerting to mobile devices in California and will soon begin testing this modality in Oregon and Washington. The Pacific Northwest presents new challenges and opportunities for ShakeAlert owing to the different types of earthquakes that occur in the Cascadia subduction zone. Many locations in the Pacific Northwest are expected to experience shaking from shallow crustal earthquakes (similar to those in California), earthquakes that occur deep within the subducted slab, and large megathrust earthquakes that occur primarily offshore. The different geometries and maximum magnitudes associated with these types of earthquakes lead to a range of warning times that are possible between when the initial ShakeAlert Message is issued and when a user experiences strong shaking. After an earthquake begins, the strategy of the ShakeAlert system for public alerting is to warn people who are located close enough to the fault that the system estimates they will experience at least weak to moderate shaking. By alerting the public at these low levels of expected shaking, it is possible to provide sufficient warning times for some users to take protective actions before strong shaking begins. In this study, we present an analysis of past ShakeAlert Messages as well as simulations of historical earthquakes and potential future Cascadia earthquakes to quantify the range of warning times that users who experience strong or worse shaking are likely to receive. Additional applications for ShakeAlert involve initiation of automatic protective actions prior to the onset of shaking, such as slowing trains, shutting water supplies, and opening firehouse doors, which are beyond the scope of this paper. Users in the Pacific Northwest should expect that the majority of alerts they receive will be from shallow crustal and intraslab earthquakes. In these cases, users will only have a few seconds of warning before strong shaking begins. This remains true even during infrequent, offshore great (magnitude ≥8) megathrust earthquakes, where warning times will generally range from seconds to tens of seconds, depending on the user’s location and the intensity of predicted shaking that a user chooses to be alerted for, with the longest warning times of 50–80 seconds possible only for users located at considerable distance from the epicenter. ShakeAlert thus requires short, readily understood alerts stating that earthquake shaking is imminent and suggesting protective actions users should take. Extensive education and outreach efforts that emphasize the need to take actions quickly will be required for ShakeAlert to successfully reduce injuries and losses.

California, Oregon, Washington↗
USGS2021

The 2018 update of the US National Seismic Hazard Model: Where, why, and how much probabilistic ground motion maps changed

The 2018 US Geological Survey National Seismic Hazard Model (NSHM) incorporates new data and updated science to improve the underlying earthquake and ground motion forecasts for the conterminous United States. The NSHM considers many new data and component input models: (1) new earthquakes between 2013 and 2017 and updated earthquake magnitudes for some earlier earthquakes; (2) two updated smoothed seismicity models to forecast earthquake rates; (3) two suites of new central and eastern US (CEUS) ground motion models (GMMs) to translate ground shaking for various earthquake sizes and source-to-site distances considered in the model; (4) two CEUS GMMs for aleatory variability; (5) two CEUS site-effect models that modify ground shaking based on alternative shallow site conditions; (6) more advanced western US (WUS) lithologic and structural information to assess basin site effects for selected urban regions; and (7) a more comprehensive range of outputs (22 periods and 8 site classes) than in previous versions of the NSHMs. Each of these new datasets and models produces changes in the probabilistic ground shaking levels that are spatially and statistically analyzed. Recent earthquakes or changes to some older earthquake magnitudes and locations mostly result in probabilistic ground shaking levels that are similar to previous models, but local changes can reach up to +80% and −60% compared to the 2014 model. Newly developed CEUS models for GMMs, aleatory variability, and site effects cause overall changes up to ±64%. The addition of the WUS basin amplifications causes changes of up to +60% at longer periods for sites overlying deep soft soils. Across the conterminous United States, the hazard changes in the model are mainly caused by new GMMs in the CEUS, by sedimentary basin effects for long periods (≥1 s) in the WUS, and by seismicity changes for short (0.2 s) and long (1 s) periods for both areas.

Earthquake Spectra↗
USGS2020

Site response, basin amplification, and earthquake stress drops in the Portland, Oregon area

Site response, sedimentary basin amplification, and earthquake stress drops for the Portland, Oregon area were determined using accelerometer recordings at 16 sites of 10 local earthquakes with M D "> M D MD 2.6–4.0. A nonlinear inversion was applied to calculate site response (0.5–10 Hz), corner frequencies, and seismic moments from the Fourier spectra of the earthquakes. Site amplifications at lower frequencies of 0.1–2.0 Hz were determined from Fourier spectra of four regional earthquakes with M w "> M w Mw 5.8–6.4. Amplifications were calculated relative to a stiff‐soil site outside the Portland and Tualatin basins. Sites on artificial fill and Holocene alluvium show strong amplification peaks (factor of 5) around 1–2 Hz. Sites on the Portland Hills, consisting of thin soil over basalt, display spectral peaks at 4–5 Hz (factor of 4). Spectral peaks at both sites are similar to those predicted for vertically propagating S waves from V S "> V S VS profiles determined at these sites using a borehole and refraction microtremor analysis. The largest amplifications at 0.1–1 Hz were found at stiff‐soil sites in the Tualatin basin, based on recordings of regional earthquakes. Amplifications of a factor of 10, at about 0.3 Hz, were observed for a site in the deeper portion of the Tualatin basin and a factor of 7 at 0.5–0.6 Hz for two adjacent sites closer to the border of that basin. Stiff‐soil sites in the Portland basin exhibit amplifications of 2–3 at frequencies of about 0.3–0.8 Hz. The frequencies of the amplification peaks for the deep Tualatin basin site can be explained by S ‐wave resonance in the shallow sediments, but the observed amplification is underestimated. Earthquake stress drops determined from the inversion range from 3 to 11 MPa, with no overall dependence on seismic moment.

Oregon↗
USGS2020

Ensemble ShakeMaps for magnitude 9 earthquakes on the Cascadia Subduction Zone

We develop ensemble ShakeMaps for various magnitude 9 ( ⁠ M "> M M 9) earthquakes on the Cascadia megathrust. Ground‐shaking estimates are based on 30 M "> M M 9 Cascadia earthquake scenarios, which were selected using a logic‐tree approach that varied the hypocenter location, down‐dip rupture limit, slip distribution, and location of strong‐motion‐generating subevents. In a previous work, Frankel et al. (2018) used a hybrid approach (i.e., 3D deterministic simulations for frequencies &lt; 1 &#x2009;&#x2009; Hz "> < 1 Hz <1 Hz and stochastic synthetics for frequencies &gt; 1 &#x2009;&#x2009; Hz "> > 1 Hz >1 Hz ⁠ ) and uniform site amplification factors to create broadband seismograms from this set of 30 earthquake scenarios. Here, we expand on this work by computing site‐specific amplification factors for the Pacific Northwest and applying these factors to the ground‐motion estimates derived from Frankel et al. (2018) . In addition, we use empirical ground‐motion models (GMMs) to expand the ground‐shaking estimates beyond the original model extent of Frankel et al. (2018) to cover all of Washington State, Oregon, northern California, and southern British Columbia to facilitate the use of these ensemble ShakeMaps in region‐wide risk assessments and scenario planning exercises. Using this updated set of 30 M "> M M 9 Cascadia earthquake scenarios, we present ensemble ShakeMaps for the median, 2nd, 16th, 84th, and 98th percentile ground‐motion intensity measures. Whereas traditional scenario ShakeMaps are based on a single hypothetical earthquake rupture, our ensemble ShakeMaps take advantage of a logic‐tree approach to estimating ground motions from multiple earthquake rupture scenarios. In addition, 3D earthquake simulations capture important features such as strong ground‐motion amplification in the Pacific Northwest’s sedimentary basins, which are not well represented in the empirical GMMs that compose traditional scenario ShakeMaps. Overall, our results highlight the importance of strong‐motion‐generating subevents for coastal sites, as well as the amplification of long‐period ground shaking in deep sedimentary basins, compared with previous scenario ShakeMaps for Cascadia.

California, Oregon, Washington↗
USGS2020

Basin amplification effects in the Puget Lowland, Washington from strong motion recordings and 3D simulations

Sedimentary basins in the Puget Sound region, Washington State, increase ground‐motion intensity and duration of shaking during local earthquakes. We analyze Pacific Northwest Seismic Network and U.S. Geological Survey strong‐motion recordings of five local earthquakes ( M 3.9–6.8), including the 2001 Nisqually earthquake, to characterize sedimentary basin effects within the Seattle and Tacoma basins. We observe basin‐edge generated surface waves at sites within the Seattle basin for most ray paths that cross the Seattle fault zone. We also note previously undocumented basin‐edge surface waves in the Tacoma basin during one of the local earthquakes. To place quantitative constraints on basin amplification, we determine amplification factors by computing the spectral ratios of inside‐basin sites to outside‐basin sites at 1, 2, 3, and 5 s periods. Ground shaking is amplified in the Seattle basin for all the earthquakes analyzed and for a subset of events in the Tacoma basin. We find that the largest amplification factors in the Seattle basin are produced by a shallow earthquake located to the southwest of the basin. Our observation suggests that future shallow crustal and megathrust earthquakes rupturing west of the Puget Lowland will produce greater amplification within the Seattle basin than has been seen for intraslab events. We also perform ground‐motion simulations using a finite‐difference method to validate a 3D Cascadia velocity model (CVM) by comparing properties of observed and synthetic waveforms up to a frequency of 1 Hz. Basin‐edge effects are well reproduced in the Seattle basin, but are less well resolved in the Tacoma basin. Continued study of basin effects in the Tacoma basin would improve the CVM.

Washington↗
USGS2020

2018 and 2023 U. S. National Seismic Hazard Models

During 2017-2018, the National Seismic Hazard Model (NSHM) was updated by incorporating (1) new median ground motion models, new estimates of their epistemic uncertainties and aleatory variabilities, and new soil amplification factors for the central and eastern U.S., (2) amplification of long-period ground motions in deep sedimentary basins in the Los Angeles, San Francisco, Seattle, and Salt Lake City areas, (3) an updated seismicity catalog, which includes new earthquakes that occurred between 2012 and 2017, and (4) improved computer code and implementation details. Results show significantly increased ground shaking in many (but not all) locations across the central and eastern U.S., and increased ground shaking in the four urban areas (listed above) that overlie deep sedimentary basins in the western U.S. During 2019-2023, the NSHM will consider additional updates for the 2023 NSHM including: 3D simulations in urban areas of Los Angeles and Seattle, additional soil amplification models for other urban areas (e.g., eastern and southern coastal plains of the U.S., Reno, and Las Vegas), non-ergodic ground motion models that reconsider epistemic and aleatory uncertainty, topographic amplification, and new geological and geodetic models for faults. These maps will be considered by the Building Seismic Safety Council, American Society of Civil Engineers, and International Building Code committees for inclusion in upcoming building codes. Due to population growth, more people live and work in areas of moderate or high seismic hazard than ever before, leading to higher risk of undesirable consequences from future ground shaking.

conterminous United States↗
USGS2019

The 2018 update of the US National Seismic Hazard Model: Overview of model and implications

During 2017–2018, the National Seismic Hazard Model for the conterminous United States was updated as follows: (1) an updated seismicity catalog was incorporated, which includes new earthquakes that occurred from 2013 to 2017; (2) in the central and eastern United States (CEUS), new ground motion models were updated that incorporate updated median estimates, modified assessments of the associated epistemic uncertainties and aleatory variabilities, and new soil amplification factors; (3) in the western United States (WUS), amplified shaking estimates of long-period ground motions at sites overlying deep sedimentary basins in the Los Angeles, San Francisco, Seattle, and Salt Lake City areas were incorporated; and (4) in the conterminous United States, seismic hazard is calculated for 22 periods (from 0.01 to 10 s) and 8 uniform V S30 maps (ranging from 1500 to 150 m/s). We also include a description of updated computer codes and modeling details. Results show increased ground shaking in many (but not all) locations across the CEUS (up to ~30%), as well as near the four urban areas overlying deep sedimentary basins in the WUS (up to ~50%). Due to population growth and these increased hazard estimates, more people live or work in areas of high or moderate seismic hazard than ever before, leading to higher risk of undesirable consequences from forecasted future ground shaking.

Earthquake Spectra↗
USGS2019

Comment on “Interpretation of Kappa and fmax filters as source effect”, by Igor A. Beresnev

Beresnev (2019) advocates the use of an earthquake slip function that produces an ω-2.5 high-frequency falloff of Fourier displacement spectra in the far field, where ω denotes the angular frequency. He argues that the observed high-frequency decay of earthquake spectra can be adequately modeled by this ω-2.5 falloff, without needing to include high frequency attenuation at shallow depth under the site, commonly characterized as fmax or kappa. In his abstract, Beresnev (2019) describes source models with falloffs intermediate between ω-2 and ω-3 as “providing natural high-cut filtering exclusively as a source effect.” In many studies to date, observed spectra are modeled using an ω-2 source spectrum combined with attenuation along the propagation path, including strong attenuation at shallow depths (< 1 km) beneath a site. It is not clear whether Beresnev (2019) is claiming that path effects (including site attenuation) are unimportant to ground motions or if he is proposing a simple, pragmatic method to fit the high-frequency decay of earthquake spectra.

Bulletin of the Seismological Society of America↗
USGS2019

Impact of down-dip rupture limit and high stress drop subevents on coseismic land-level change during Cascadia megathrust earthquakes

Seismic hazard associated with Cascadia megathrust earthquakes is strongly dependent on the landward rupture extent and heterogeneous fault properties. We use 3-D numerical simulations and a seismic velocity model for Cascadia to estimate coseismic deformation due to ~M9 earthquake scenarios. Our earthquake source model is based on observations of the 2010 M8.8 Maule and 2011 M9.0 Tohoku earthquakes, which exhibited distinct strong-motion-generating subevents in the deeper portions of the fault. We compare our estimates for land-level change to paleoseismic estimates for coseismic coastal subsidence during the A.D. 1700 Cascadia earthquake. Results show that megathrust rupture extending to the 1 cm/yr locking contour provides a good match to geologic data, and along-strike variations in coastal subsidence can be produced by including strong-motion-generating subevents in the down-dip regions of the megathrust. This work demonstrates the potential to improve seismic hazard estimates for Cascadia earthquakes by comparing physics-based earthquake simulations with geologic observations.

Cascadian Fault↗
USGS2019

Impacts of simulated M9 Cascadia Subduction Zone motions on idealized systems

Ground motions have been simulated for a magnitude 9 (M9) Cascadia Subduction Zone earthquake, which will affect the Puget Lowland region, including cities underlain by the Seattle, Everett, and Tacoma sedimentary basins. The current national seismic maps do not account for the effects of these basins on the risk-targeted Maximum Considered Earthquake (MCE R ). The simulated motions for Seattle had large spectral accelerations (at a period of 2 s, 43% of simulated M9 motions exceeded the MCE R ), damaging spectral shapes (particularly at periods near 1 s), and long durations (5%–95% significant durations near 110 s). For periods of 1 s or longer, the resulting deformation demands and collapse likelihood for four sets of single-degree-of-freedom systems exceeded the corresponding values for motions consistent with the conditional mean spectra at the MCE R intensity (MCE R ). The regional variation of damage was estimated by combining probabilistic characterizations of the seismic resistance of structures and of the effective spectral acceleration, S a,eff , which accounts for the effects of spectral acceleration, spectral shape, and ground-motion duration. For high-strength, low-ductility systems located above deep basins ( Z 2.5 > 6 km), the likelihood of collapse during an M9 earthquake averaged 13% and 18% at 1.0 s and 2.0 s periods, respectively. For low-strength, high-ductility systems, the corresponding likelihoods of collapse averaged 18% and 7%.

Washington↗
USGS2019

Source-dependent amplification of earthquake ground motions in deep sedimentary basins

Deep sedimentary basins amplify long-period shaking from seismic waves, increasing the seismic hazard for cities within such basins. We perform 3-D simulations of point source earthquakes distributed around the Seattle and Tacoma basins in Washington State, to examine the dependence of basin amplification on source azimuth, depth, and earthquake type. For periods between 1-10 s, the pattern of amplification is spatially heterogeneous and differs considerably with the source-to-site azimuth. For close-in earthquakes, the greatest basin amplification occurs towards the far side of the basin and ground motions from crustal earthquakes experience greater amplification than those from more vertically-incident, deeper intraplate earthquakes. Love and Rayleigh waves form similar spatial patterns for a given source location, although the magnitude of amplification varies. The source dependence of basin amplification is an important factor for seismic hazard assessment, both in the Seattle and Tacoma basins, and by extension for deep sedimentary basins worldwide.

Washington↗
USGS2018

2018 report on incorporating sedimentary basin response into the design of tall buildings in Seattle, Washington

On March 22, 2018, the Seattle Department of Construction and Inspections (SDCI) and the U.S. Geological Survey (USGS) convened a workshop of engineers and seismologists to provide guidance on incorporating sedimentary basin response into the design of tall buildings in Seattle. This workshop provided recommendations that build on those from a March 2013 workshop (Chang and others, 2014), primarily based on new results from 3-D simulations of magnitude (M) 9 Cascadia earthquakes (The M9 Project). Susan Chang, a geotechnical engineer with the Seattle Department of Construction and Inspections, organized and led the workshop; Art Frankel (USGS) assisted in constructing the agenda. The workshop agenda and attendees are provided in the appendix. The attendees represented a wide range of expertise, including seismologists with expertise in ground motions and basin response, geotechnical engineers, and structural engineers. Their professional experience included working on local projects related to the design of long-period structures; peer reviewing ground motions for performance-based design of high-rises in Seattle; researching basin response in academic, government and industry settings; developing ground motion models; and representing local and national structural engineering organizations. In this report, we summarize the technical presentations, key discussion points, and recommendations from the workshop.

Washington↗
USGS2018

Broadband synthetic seismograms for magnitude 9 earthquakes on the Cascadia Megathrust based on 3D simulations and stochastic synthetics, Part 2: Rupture parameters and variability

We used a combination of 3D finite‐difference simulations ( &lt; 1 &#x2009;&#x2009; Hz "> < 1 Hz ) and 1D stochastic synthetics ( &gt; 1 &#x2009;&#x2009; Hz "> > 1 Hz ) to generate broadband (0–10 Hz) synthetic seismograms for numerous M w "> Mw 9 earthquake rupture scenarios on the Cascadia megathrust. Slip consists of multiple high‐stress‐drop subevents ( M w "> Mw 8) with short rise times on the deeper portions of the fault, superimposed on a background slip distribution with longer rise times. We identify key rupture parameters that control the intensity of ground shaking and resulting seismic hazard; these include the hypocenter location, the down‐dip limit of slip, the average rupture velocity, and the character (i.e., location, magnitude, and stress drop) of subevents. Extending the down‐dip limit of rupture to the top of the nonvolcanic tremor zone results in localized regions with a factor of 5–10 increase in spectral acceleration (SA) for periods &lt; 5 &#x2009;&#x2009; s "> <5 s , compared to a rupture that is completely offshore. This is primarily due to the closer proximity of high‐stress‐drop subevents to inland locations when the rupture is allowed to extend deeper. Similarly, we find that the hypocenter location can result in a variation in the intensity of ground motions of a factor of &gt; 10 "> >10 , due to the effects of rupture directivity (i.e., SA at periods &gt; 1 &#x2009;&#x2009; s "> >1 s ). We also observe a coupling between rupture directivity and basin amplification. The intensity of ground motions is also strongly affected by the magnitude, stress drop, and location of high‐stress‐drop subevents, which are poorly constrained. Overall, our results quantify the effect of kinematic rupture parameters on ground motions for an M w "> Mw 9 earthquake in Cascadia and emphasize the need for further constraints on these parameters to improve seismic hazard estimates in the Pacific Northwest.

Bulletin of the Seismological Society of America↗
USGS2018

Broadband synthetic seismograms for magnitude 9 earthquakes on the Cascadia megathrust based on 3D simulations and stochastic synthetics, part 1: Methodology and overall results

We have produced a large set of broadband (0–10 Hz) synthetic seismograms for Mw 9.0 earthquakes on the Cascadia megathrust by combining synthetic seismograms derived from 3D finite‐difference simulations ( ⁠≤1 Hz⁠ ) with finite‐source, stochastic synthetics ( ⁠≥1 Hz⁠ ). We used a compound rupture model consisting of high stress drop M w 8 subevents superimposed on large, shallower slip with long‐slip duration, informed by observations of the M w 9.0 Tohoku, Japan, and M w 8.8 Maule, Chile, earthquakes. Thirty 3D simulations were run, considering a variety of rupture parameters, to determine the range of expected ground motions. For sites not in sedimentary basins, the spectral accelerations of the synthetics are similar to the BC Hydro ground‐motion prediction equations (GMPEs) for periods of 0.1–6 s, but exceed them at periods greater than 6 s. Response spectra from the synthetics at sites in the Seattle and Tacoma sedimentary basins show large amplifications of factors of 2–5 at periods of 1–10 s. This basin amplification is substantially larger than that found for crustal earthquakes in the Next Generation Attenuation‐West2 (NGA‐West2) GMPEs. Basin amplification is caused by basin‐edge generated surface waves and by amplification and focusing of S waves and surface waves by the 3D basin structure. The synthetic seismograms show effective average durations of strong motions of about 70 s for coastal sites, increasing to about 120 s at 200 km distance. We find that the interevent and intraevent standard deviations of the spectral amplitudes of the synthetics are larger for sites closer to the rupture, because they are more sensitive to the location of subevents and rupture directivity.

California, Oregon, Washington↗
USGS2018

Integrate urban‐scale seismic hazard analyses with the U.S. National Seismic Hazard Model

For more than 20 yrs, damage patterns and instrumental recordings have highlighted the influence of the local 3D geologic structure on earthquake ground motions (e.g., M "> M M 6.7 Northridge, California, Gao et al. , 1996 ; M "> M M 6.9 Kobe, Japan, Kawase, 1996 ; M "> M M 6.8 Nisqually, Washington, Frankel, Carver, and Williams, 2002 ). Although this and other local‐scale features are critical to improving seismic hazard forecasts, historically they have not been explicitly incorporated into the U.S. National Seismic Hazard Model (NSHM, national model and maps), primarily because the necessary basin maps and methodologies were not available at the national scale. Instead, the U.S. Geological Survey (USGS), its partners, and external groups developed urban seismic hazard maps (urban models and maps) that consider detailed site effects in local areas (e.g., Wong et al. , 2002 ; Cramer et al. , 2006 ; Frankel et al. , 2007 ; Graves et al. , 2011 ). The disconnect between the urban and national hazard models, however, means that the national models, which underlie U.S. building codes and other applications, do not make use of all of the scientific results informing earthquake ground‐shaking hazards. We recommend that future U.S. national seismic hazard assessment make use of all available regional information, including that in urban models. In this column, we describe the roles of and differences between the urban and national models, and discuss the obstacles to and benefits of integrating the urban models with the national model. Future progress on this issue will require further coordination and implementation efforts between the USGS and external partners.

Seismological Research Letters↗
USGS2018

The science, engineering applications, and policy implications of simulation-based PSHA

We summarize scientific methods for developing probabilistic seismic hazard assessments from 3-D earthquake ground motion simulations, describe current use of simulated ground motions for engineering applications, and discuss on-going efforts to incorporate these effects in the U.S. national seismic hazard model. The 3-D simulations provide important, additional information about earthquake ground-shaking, which is critical to proper characterization of potential ground motions. Example uses of these simulations for engineering applications provide alternative approaches to introducing the effects of deep basins on long-period ground motions into design requirements. In Seattle, Washington tall building design includes requirements for accounting for the effect of the Seattle basin, and one method for including this effect relies upon local 3-D simulations. In Los Angeles, California a working group of scientists and engineers is advancing the use of local 3-D simulations for local building codes. In light of the benefit to ground motion characterization from the use of 3-D simulations, similar efforts are underway for national-scale seismic hazard analyses, which seek to make use of the extensive work applied from local efforts; current methods for incorporating these effects on a national-scale are presented.

Conference Paper↗