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.

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.

30 Ooctober 2020 Samos-Sigacik Earthquake: On Strong Ground Motion and Local Site Amplification

2021 ◽  
Author(s):  
Eser Çakti ◽  
Karin Sesetyan ◽  
Ufuk Hancilar ◽  
Merve Caglar ◽  
Emrullah Dar ◽  
...  
Keyword(s):  
Ground Motion ◽  
Structural Damage ◽  
Strong Ground Motion ◽  
Epicentral Distance ◽  
Strong Motion ◽  
Aegean Sea ◽  
Site Amplification ◽  
Local Site ◽  
Basin Effects ◽  
Strong Ground

<p>The Mw 6.9 earthquake that took place offshore between the Greek island of Samos and Turkey’s İzmir province on 30 October 2020 came hardly as a surprise. Due to the extensional tectonic regime of the Aegean and high deformation rates, earthquakes of similar size frequently occur in the Aegean Sea on fault segments close to the shores of Turkey, affecting the settlements on mainland Turkey and on the Greek Islands. Samos-Sigacik earthquake had a normal faulting mechanism. It was recorded by the strong motion networks in Turkey and Greece. Although expected, the earthquake was an  outstanding event in the sense of  highly localized, significant levels of building damage as a result of amplified ground motion levels. This presentation is an overview of strong ground motion characteristics of this important event both regionally and locally. Mainshock records suggest that local site effects, enhanced by basin effects could be responsible for structural damage in central Izmir, the third largest city of Turkey located at 60-70 km epicentral distance. We installed a seven-station network in Bayraklı and Karşıyaka districts of İzmir within three days of the mainshock in search of site and basin effects.  Through analysis of recorded aftershocks we explore the amplification characeristics of soils in the two aforementioned districts  and try to understand the role basin effects might have played in the resulting ground motion levels and consequently damage. </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.

Surface-wave dispersion analysis in Mexico City

1995 ◽  
Vol 85 (4) ◽  
pp. 1116-1126
Author(s):  
Francisco J. Chávez-García ◽  
Jaime Ramos-Martínez ◽  
Evangelina Romero-Jiménez
Keyword(s):  
Surface Wave ◽  
Surface Waves ◽  
Ground Motion ◽  
Mexico City ◽  
Rayleigh Waves ◽  
Strong Motion ◽  
Clay Layer ◽  
Period Range ◽  
Wave Trains ◽  
Refraction Data

Abstract In this article, we present an observational investigation of ground motion at Mexico City focused on surface waves. Our purpose is 2-fold; first, to understand incident ground motion during the great Michoacán earthquake of 19 September 1985, and second, to characterize surface waves propagating in the lake-bed zone. To this end we analyze the strong-motion records obtained at Mexico City for the large (MS = 8.1) earthquake of 19 September 1985. It is shown that, in the low-frequency range, we observe the Rayleigh fundamental mode in both the vertical and the radial components, and the Love fundamental mode in the transverse component at all the strong-motion stations. The vertical component also shows the first higher mode of Rayleigh waves. We use a very broadband record obtained at station CU for the smaller (MS = 6.7) earthquake of 14 May 1993 to verify that the dispersion computed from the model of Campillo et al. (1989) represents well the average surface-wave propagation between the coast and Mexico City in the 7- to 10-sec period range. We use this result to assign absolute times to the strong-motion records of the Michoacán event. This allowed us to identify additional wave trains that propagate laterally in directions other than great circle in the 3- to 5-sec period range. These wave trains are identified as Love waves. In a second analysis, we study a set of refraction data obtained during a small-scale (250 m) experiment on the virgin clay of the lake-bed zone. Phase-velocity dispersion curves for several modes of Rayleigh waves are identified in the refraction data and inverted to obtain an S-wave velocity profile. This profile is used as the uppermost layering in a 2D model of Mexico City valley. The results of numerical simulation show that surface waves generated by lateral finiteness of the clay layer suffer large dispersion and attenuation. We conclude that surface waves generated by the lateral heterogeneity of the upper-most stratigraphy very significantly affect ground motion near the edge of the valley, but their importance is negligible for distances larger than 1.5 km from the edge. Thus, locally generated surface waves propagating through the clay layer cannot explain late arrivals observed for the 1985 event. We suggest that the long duration of strong motion is due to the interaction between lateral propagation of waves guided by deep layers (1 to 4 km) and the surficial clay layer. This interaction is possible by the coincidence of the dominant frequency of the uppermost layers and the frequency of the deeply guided waves.

Quantification of the Influence of Deep Basin Effects on Structural Collapse Using SCEC CyberShake Earthquake Ground Motion Simulations

2019 ◽  
Vol 35 (4) ◽  
pp. 1845-1864 ◽  
Author(s):  
Nenad Bijelić ◽  
Ting Lin ◽  
Gregory G. Deierlein
Keyword(s):  
Los Angeles ◽  
Ground Motion ◽  
Ground Motions ◽  
Sedimentary Basins ◽  
Earthquake Ground Motion ◽  
Structural Collapse ◽  
Deep Basin ◽  
Intensity Measures ◽  
Significant Duration ◽  
Basin Effects

This paper examines the effects of earthquake ground motions in deep sedimentary basins on structural collapse risk using physics-based earthquake simulations of the Los Angeles basin developed through the Southern California Earthquake Center's CyberShake project. Distinctive waveform characteristics of deep basin seismograms are used to classify the ground motions into several archetype groups, and the damaging influence of the basin effects are evaluated by comparing nonlinear structural responses under spectrum and significant duration equivalent basin and nonbasin ground motions. The deep basin ground motions are observed to have longer period-dependent durations and larger sustained spectral intensities than nonbasin motions for vibration periods longer than about 1.5 s, which can increase structural collapse risk by up to 20% in ground motions with otherwise comparable peak spectral accelerations and significant durations. Two new metrics are proposed to quantify period-dependent duration effects that are not otherwise captured by conventional ground motion intensity measures. The proposed sustained amplitude response spectra and significant duration spectra show promise for characterizing the damaging effects of long duration features of basin ground motions on buildings and other structures.

scholarly journals Design strategies to achieve target collapse risks for reinforced concrete wall buildings in sedimentary basins

2020 ◽  
Vol 36 (3) ◽  
pp. 1038-1073 ◽  
Author(s):  
Nasser A Marafi ◽  
Andrew J Makdisi ◽  
Jeffrey W Berman ◽  
Marc O Eberhard
Keyword(s):  
Reinforced Concrete ◽  
Seismic Hazard ◽  
Ground Motion ◽  
Sedimentary Basins ◽  
Design Strategies ◽  
Concrete Wall ◽  
Cross Sectional ◽  
Drift Capacity ◽  
Basin Effects ◽  
Reinforced Concrete Wall

Studies of recorded ground motions and simulations have shown that deep sedimentary basins can greatly increase the damage expected during earthquakes. Unlike past earthquake design provisions, future ones are likely to consider basin effects, but the consequences of accounting for these effects are uncertain. This article quantifies the impacts of basin amplification on the collapse risk of 4- to 24-story reinforced concrete wall building archetypes in the uncoupled direction. These buildings were designed for the seismic hazard level in Seattle according to the ASCE 7-16 design provisions, which neglect basin effects. For ground motion map frameworks that do consider basin effects (2018 USGS National Seismic Hazard Model), the average collapse risk for these structures would be 2.1% in 50 years, which exceeds the target value of 1%. It is shown that this 1% target could be achieved by: (1) increasing the design forces by 25%, (2) decreasing the drift limits from 2.0% to 1.25%, or (3) increasing the median drift capacity of the gravity systems to exceed 9%. The implications for these design changes are quantified in terms of the cross-sectional area of the walls, longitudinal reinforcement, and usable floor space. It is also shown that the collapse risk increases to 2.8% when the results of physics-based ground motion simulations are used for the large-magnitude Cascadia subduction interface earthquake contribution to the hazard. In this case, it is necessary to combine large changes in the drift capacities, design forces, and/or drift limits to meet the collapse risk target.

Observed Variation of Earthquake Motion across a Basin—Taipei City

1998 ◽  
Vol 14 (1) ◽  
pp. 115-133 ◽  
Author(s):  
Chin-Hsiung Loh ◽  
Jeng-Yaw Hwang ◽  
Tzay-Chyn Shin
Keyword(s):  
Ground Motion ◽  
Seismic Waves ◽  
Principal Direction ◽  
Response Spectrum ◽  
Strong Motion ◽  
Seismic Source ◽  
Spectral Ratio ◽  
Site Amplification ◽  
Taipei Basin ◽  
Basin Effects

Local site amplification of sedimentary deposit during earthquakes is an important issue in strong ground motion analysis. The phenomenon is more obvious for sediment basin. From the strong-motion instrumentation network of Taipei basin, the ground motion characteristics of the basin effects are studied from two seismic events: the June 5, 1994 earthquake with ML = 6.57 and the June 25, 1995 earthquake with ML = 6.50. The objective is to investigate the effects of the basin structure on the patterns of the recorded ground motions. The analyses include: (1) response spectrum and spectral ratio analyses; (2) correlation of seismic source, PGA distribution and strong-motion duration with site amplification, (3) principal direction analysis of seismic waves in the basin. The observed variations of ground motion across the basin are different from each other because of the basin effect. It means that for the Taipei basin, the basin effects for shallow sources are going to be much more significant than for the deep sources.

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