Ensemble ShakeMaps for Magnitude 9 Earthquakes on the Cascadia Subduction Zone

2020 ◽  
Vol 92 (1) ◽  
pp. 199-211
Author(s):  
Erin A. Wirth ◽  
Alex Grant ◽  
Nasser A. Marafi ◽  
Arthur D. Frankel
Keyword(s):  
Ground Motion ◽  
Strong Motion ◽  
Sedimentary Basins ◽  
Earthquake Rupture ◽  
Logic Tree ◽  
Ground Shaking ◽  
Amplification Factors ◽  
Earthquake Scenarios ◽  
The Pacific ◽  
Tree Approach

Abstract We develop ensemble ShakeMaps for various magnitude 9 (M 9) earthquakes on the Cascadia megathrust. Ground-shaking estimates are based on 30 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 <1  Hz and stochastic synthetics for frequencies >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 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.

Basin Amplification Effects in the Puget Lowland, Washington, from Strong-Motion Recordings and 3D Simulations

2020 ◽  
Vol 110 (2) ◽  
pp. 534-555 ◽  
Author(s):  
Mika Thompson ◽  
Erin A. Wirth ◽  
Arthur D. Frankel ◽  
J. Renate Hartog ◽  
John E. Vidale
Keyword(s):  
Surface Waves ◽  
Ground Motion ◽  
Puget Sound ◽  
Strong Motion ◽  
Sedimentary Basins ◽  
Amplification Factors ◽  
Megathrust Earthquakes ◽  
Local Earthquakes ◽  
Basin Effects ◽  
Basin Edge

ABSTRACT 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.

scholarly journals Earthquake ground shaking hazard assessment for the Lower Hutt and Porirua areas, New Zealand

1992 ◽  
Vol 25 (4) ◽  
pp. 286-302 ◽  
Author(s):  
R. J. Van Dissen ◽  
J. J. Taber ◽  
W. R. Stephenson ◽  
S. Sritheran ◽  
S. A. L. Read ◽  
...  
Keyword(s):  
Ground Motion ◽  
Strong Motion ◽  
Spectral Ratio ◽  
Fine Sand ◽  
Geographic Variations ◽  
Ground Acceleration ◽  
Ground Shaking ◽  
Earthquake Scenarios ◽  
Shear Wave Velocities ◽  
Strong Ground

Geographic variations in strong ground shaking expected during damaging earthquakes impacting on the Lower Hutt and Porirua areas are identified and quantified. Four ground shaking hazard zones have been mapped in the Lower Hutt area, and three in Porirua, based on geological, weak motion, and strong motion inputs. These hazard zones are graded from 1 to 5. In general, Zone 5 areas are subject to the greatest hazard, and Zone 1 areas the least. In Lower Hutt, zones 3 and 4 are not differentiated and are referred to as Zone 3-4. The five-fold classification is used to indicate the range of relative response. Zone 1 areas are underlain by bedrock. Zone 2 areas are typically underlain by compact alluvial and fan gravel. Zone 3-4 is underlain, to a depth of 20 m, by interfingered layers of flexible (soft) sediment (fine sand, silt, clay, peat), and compact gravel and sand. Zone 5 is directly underlain by more than 10 m of flexible sediment with shear wave velocities in the order of 200 m/s or less. The response of each zone is assessed for two earthquake scenarios. Scenario 1 is for a moderate to large, shallow, distant earthquake that results in regional Modified Mercalli intensity V-VI shaking on bedrock. Scenario 2 is for a large, local, but rarer, Wellington fault earthquake. The response characterisation for each zone comprises: expected Modified Mercalli intensity; peak horizontal ground acceleration; duration of strong shaking; and amplification of ground motion with respect to bedrock, expressed as a Fourier spectral ratio, including the frequency range over which the most pronounced amplification occurs. In brief, high to very high ground motion amplifications are expected in Zone 5, relative to Zone 1, during a scenario 1 earthquake. Peak Fourier spectral ratios of 10-20 are expected in Zone 5, relative to Zone 1, and a difference of up to three, possibly four, MM intensity units is expected between the two zones. During a scenario 2 event, it is anticipated that the level of shaking throughout the Lower Hutt and Porirua region will increase markedly, relative to scenario 1, and the average difference in shaking between each zone will decrease.

Modeling the Impact of Earthquake-Induced Debris on Tsunami Evacuation Times of Coastal Cities

2019 ◽  
Vol 35 (1) ◽  
pp. 137-158 ◽  
Author(s):  
Sebastián Castro ◽  
Alan Poulos ◽  
Juan Carlos Herrera ◽  
Juan Carlos de la Llera
Keyword(s):  
Ground Motion ◽  
Population Increase ◽  
Ground Shaking ◽  
Agent Based ◽  
Earthquake Scenarios ◽  
Coastal Cities ◽  
Increased Risk ◽  
Geographical Regions ◽  
Evacuation Routes ◽  
The Impact

Tsunami alerts following severe earthquakes usually affect large geographical regions and require people to evacuate to higher safety zones. However, evacuation routes may be hindered by building debris and vehicles, thus leading to longer evacuation times and an increased risk of loss of life. Herein, we apply an agent-based model to study the evacuation situation of the coastal city of Iquique, north Chile, where most of the population is exposed to inundation from an incoming tsunami. The study evaluates different earthquake scenarios characterized by different ground motion intensities in terms of the evacuation process within a predefined inundation zone. Evacuating agents consider the microscale interactions with cars and other people using a collision avoidance algorithm. Results for the no ground shaking scenario are compared for validation with those of a real evacuation drill done in 2013 for the entire city. Finally, a parametric analysis is performed with ten different levels of ground motion intensity, showing that evacuation times for 95% of the population increase in 2.5 min on average when considering the effect of building debris.

Spatial Variability of Source and Attenuation Characteristics in Large Ground-Motion Datasets

2020 ◽  
Author(s):  
Sreeram Reddy Kotha ◽  
Graeme Weatherill ◽  
Dino Bindi ◽  
Fabrice Cotton
Keyword(s):  
Spatial Variability ◽  
Ground Motion ◽  
Ground Motions ◽  
Low Frequency ◽  
Strong Motion ◽  
Response Spectra ◽  
Large Datasets ◽  
Earthquake Scenarios ◽  
Crustal Earthquakes ◽  
Geographical Regions

<p>Ground-Motion Models (GMMs) characterize the random distributions of ground-motions for a combination of earthquake source, wave travel-path, and the effected site’s geological properties. Typically, GMMs are regressed over a compendium of strong ground-motion recordings collected from several earthquakes recorded at multiple sites scattered across a variety of geographical regions. The necessity of compiling such large datasets is to expand the range of magnitude, distance, and site-types; in order to regress a GMM capable of predicting realistic ground-motions for rare earthquake scenarios, e.g. large magnitudes at short distances from a reference rock site. The European Strong-Motion (ESM) dataset is one such compendium of observations from a few hundred shallow crustal earthquakes recorded at a several hundred seismic stations in Europe and Middle-East.</p><p>We developed new GMMs from the ESM dataset, capable of predicting both the response spectra and Fourier spectra in a broadband of periods and frequencies, respectively. However, given the clear tectonic and geological diversity of the data, possible regional and site-specific differences in observed ground-motions needed to be quantified; whilst also considering the possible contamination of data from outliers. Quantified regional differences indicate that high-frequency ground-motions attenuate faster with distance in Italy compared to the rest of Europe, as well as systematically weaker ground-motions from central Italian earthquakes. In addition, residual analyses evidence anisotropic attenuation of low frequency ground-motions, imitating the pattern of shear-wave energy radiation. With increasing spatial variability of ground-motion data, the GMM prediction variability apparently increases. Hence, robust mixed-effects regressions and residual analyses are employed to relax the ergodic assumption.</p><p>Large datasets, such as the ESM, NGA-West2, and from KiK-Net, provide ample opportunity to identify and evaluate the previously hypothesized event-to-event, region-to-region, and site-to-site differences in ground-motions. With the appropriate statistical methods, these variabilities can be quantified and applied in seismic hazard and risk predictions. We intend to present the new GMMs: their development, performance and applicability, prospective improvements and research needs.</p>

First‐Order Mantle Subduction‐Zone Structure Effects on Ground Motion: The 2016 Mw 7.1 Iniskin and 2018 Mw 7.1 Anchorage Earthquakes

2019 ◽  
Vol 91 (1) ◽  
pp. 85-93 ◽  
Author(s):  
Michael Everett Mann ◽  
Geoffrey A. Abers
Keyword(s):  
Ground Motion ◽  
Strong Motion ◽  
Zone Structure ◽  
Kenai Peninsula ◽  
Ground Shaking ◽  
Intermediate Depth ◽  
First Order ◽  
Basin Effects ◽  
Order Of Magnitude ◽  
Back Arc

Abstract The 24 January 2016 Iniskin, Alaska earthquake, at Mw 7.1 and 111 km depth, is the largest intermediate‐depth earthquake felt in Alaska, with recorded accelerations reaching 0.2g near Anchorage. Ground motion from the Iniskin earthquake is underpredicted by at least an order of magnitude near Anchorage and the Kenai Peninsula, and is similarly overpredicted in the back‐arc north and west of Cook Inlet. This is in strong contrast to the 30 November 2018 earthquake near Anchorage that was also Mw 7.1 but only 48 km deep. The Anchorage earthquake signals show strong distance decay and are generally well predicted by ground‐motion prediction equations. Smaller intermediate‐depth earthquakes (depth>70  km and 3<M<6.4) with hypocenters near the Iniskin mainshock show similar patterns in ground shaking as the Iniskin earthquake, indicating that the shaking pattern is due to path effects and not the source. The patterns indicate a first‐order role for mantle attenuation in the spatial variability of strong motion. In addition, along‐slab paths appear to be amplified by waveguide effects due to the subduction of crust at >1  Hz; the Anchorage and Kenai regions are particularly susceptible to this amplification due to their fore‐arc position. Both of these effects are absent in the 2018 Anchorage shaking pattern, because that earthquake is shallower and waves largely propagate in the upper‐plate crust. Basin effects are also present locally, but these effects do not explain the first‐order amplitude variations. These analyses show that intermediate‐depth earthquakes can pose a significant shaking hazard, and the pattern of shaking is strongly controlled by mantle structure.

Survey of Fragile Geologic Features and Their Quasi-Static Earthquake Ground-Motion Constraints, Southern Oregon

2021 ◽  
Author(s):  
Devin McPhillips ◽  
Katherine M. Scharer
Keyword(s):  
Ground Motion ◽  
Pacific Northwest ◽  
Field Measurements ◽  
Point Clouds ◽  
Earthquake Ground Motion ◽  
Ground Shaking ◽  
Motion Constraints ◽  
Megathrust Earthquakes ◽  
The Pacific ◽  
Rock Pillars

ABSTRACT Fragile geologic features (FGFs), which are extant on the landscape but vulnerable to earthquake ground shaking, may provide geological constraints on the intensity of prior shaking. These empirical constraints are particularly important in regions such as the Pacific Northwest that have not experienced a megathrust earthquake in written history. Here, we describe our field survey of FGFs in southern Oregon. We documented 58 features with fragile geometric characteristics, as determined from field measurements of size and strength, historical photographs, and light detection and ranging point clouds. Among the surveyed FGFs, sea stacks have particular advantages for use as ground-motion constraints: (1) they are frequently tall and thin; (2) they are widely distributed parallel to the coast, proximal to the trench and the likely megathrust rupture surface; and (3) they are formed by sea cliff retreat, meaning that their ages may be coarsely estimated as a function of distance from the coast. About 40% of the surveyed sea stacks appear to have survived multiple Cascadia megathrust earthquakes. Using a quasi-static analysis, we estimate the minimum horizontal ground accelerations that could fracture the rock pillars. We provide context for the quasi-static results by comparing them with predictions from kinematic simulations and ground-motion prediction equations. Among the sea stacks old enough to have survived multiple megathrust earthquakes (n = 16), eight yield breaking accelerations lower than the predictions, although they generally overlap within uncertainty. FGFs with the lowest breaking accelerations are distributed uniformly over 130 km of coastline. Results for inland features, such as speleothems, are in close agreement with the predictions. We conclude that FGFs show promise for investigating both past earthquake shaking and its spatial variability along the coasts of Oregon and Washington, where sea stacks are often prevalent. Future work can refine our understanding of FGF age and evolution.

scholarly journals On the modeling of strong motion parameters and correlation with historical macroseismic data: an application to the 1915 Avezzano earthquake

1995 ◽  
Vol 38 (5-6) ◽  
Author(s):  
R. Berardi ◽  
A. Mendez ◽  
M. Mucciarelli ◽  
F. Pacor ◽  
G. Longhi ◽  
...  
Keyword(s):  
Ground Motion ◽  
Goodness Of Fit ◽  
Strong Motion ◽  
Seismic Energy ◽  
Rupture Process ◽  
Macroseismic Data ◽  
Motion Modeling ◽  
Ground Shaking ◽  
Acceleration Time Histories ◽  
Motion Parameters

This article describes the results of a ground motion modeling study of the 1915 Avezzano earthquake. The goal was to test assuinptions regarding the rupture process of this earthquake by attempting to model the damage to historical monuments and populated habitats during the earthquake. The methodology used combines stochastic and deterministic modeling techniques to synthesize strong ground motion, starting from a simple characterization of the earthquake source on an extended fault plane. The stochastic component of the methodology is used to simulate high-frequency ground motion oscillations. The envelopes of these synthetic waveforms, however, are simulated in a deterministic way based on the isochron formulation for the calculation of radiated seismic energy. Synthetic acceleration time histories representative of ground motion experienced at the towns of Avezzano, Celano, Ortucchio, and Sora are then analyzed in terms of the damage to historical buildings at these sites. The article also discusses how the same methodology can be adapted to efficiently evaluate various strong motion parameters such as duration and amplitude of ground shaking, at several hundreds of surface sites and as a function of rupture process. The usefulness of such a technique is illustrated through the inodeling of intensity data from the Avezzano earthquake. One of the most interesting results is that it is possible to distinguish between different rupture scenarios for the 1915 earthquake based on the goodness of fit of theoretical intensities to observed values.

Partitioning Ground Motion Uncertainty When Conditioned on Station Data

2022 ◽  
Author(s):  
Davis T. Engler ◽  
C. Bruce Worden ◽  
Eric M. Thompson ◽  
Kishor S. Jaiswal
Keyword(s):  
Ground Motion ◽  
Strong Motion ◽  
Macroseismic Intensity ◽  
Observational Constraints ◽  
Ground Shaking ◽  
Ground Failure ◽  
Strong Motion Station ◽  
Station Data ◽  
Uncertainty Estimates ◽  
The World

ABSTRACT Rapid estimation of earthquake ground shaking and proper accounting of associated uncertainties in such estimates when conditioned on strong-motion station data or macroseismic intensity observations are crucial for downstream applications such as ground failure and loss estimation. The U.S. Geological Survey ShakeMap system is called upon to fulfill this objective in light of increased near-real-time access to strong-motion records from around the world. Although the station data provide a direct constraint on shaking estimates at specific locations, these data also heavily influence the uncertainty quantification at other locations. This investigation demonstrates methods to partition the within- (phi) and between-event (tau) uncertainty estimates under the observational constraints, especially when between-event uncertainties are heteroscedastic. The procedure allows the end users of ShakeMap to create separate between- and within-event realizations of ground-motion fields for downstream loss modeling applications in a manner that preserves the structure of the underlying random spatial processes.

scholarly journals Stand-Alone Tsunami Alarm Equipment

2016 ◽  
Author(s):  
Akio Katsumata ◽  
Yutaka Hayashi ◽  
Kazuki Miyaoka ◽  
Hiroaki Tsushima ◽  
Toshitaka Baba ◽  
...  
Keyword(s):  
Ground Motion ◽  
Low Cost ◽  
Strong Motion ◽  
Source Area ◽  
Single Site ◽  
Peak Displacement ◽  
Ground Shaking ◽  
Mems Accelerometer ◽  
Current Location ◽  
Strong Ground

Abstract. One of the quickest means of tsunami evacuation is transfer to higher ground soon after strong and long ground-shaking. Strong ground motion means that the source area of the event is close to the current location, and long ground-shaking or large displacement means that the magnitude is large. We investigated the possibility to apply this to tsunami hazard alarm using single-site ground motion observation. Information from the mass media may not be available sometimes due to power failure. Thus, a device that indicates risk of a tsunami without referring to data elsewhere would be helpful to those should evacuate. Since the sensitivity of a low-cost MEMS accelerometer is sufficient for this purpose, tsunami alarms equipment for home use may be easily realized. Several observation values (e.g., strong-motion duration, peak ground displacement) were investigated as candidates. It was found that a suitable value for a single-site tsunami alarm is long-period peak displacement or the product of strong-motion duration and peak displacement. It was possible to detect an earthquake with a magnitude greater than 7.8 with a 0.8 threat score. Application of this method to recent major earthquakes indicated that such equipment could effectively alert people to the possibility of tsunami.

Study on Strong Motion Records Database and Selection Methods

2012 ◽  
Vol 256-259 ◽  
pp. 2117-2121
Author(s):  
Li Lin ◽  
Rui Zhi Wen ◽  
Bao Feng Zhou ◽  
Da Cheng Shi
Keyword(s):  
Ground Motion ◽  
Earthquake Engineering ◽  
Strong Motion ◽  
Selection Methods ◽  
Strong Motion Records ◽  
Engineering Research ◽  
Conditional Mean Spectrum ◽  
Great Earthquakes ◽  
The Pacific ◽  
Ground Motion Records

In this paper, PEER Ground Motion Databases (PGMD) at the Pacific Earthquake Engineering Research Center (PEER) was updated by 314 sets of ground motion records of great earthquakes in recent years, which expanded the application of this database. This paper reviews alternative selection methods for strong ground motion records. The expanded database could make the different selection and scaling of strong motion records in great earthquakes, and the conditional mean spectrum (CMS) method could be applied for the strong motion records selection in structural spectrum analysis.

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