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.

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>

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.

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.

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.

scholarly journals The ShakeMaps of the Amatrice, M6, earthquake

2016 ◽  
Vol 59 ◽  
Author(s):  
Licia Faenza ◽  
Valentino Lauciani ◽  
Alberto Michelini
Keyword(s):  
Ground Motion ◽  
Data Exchange ◽  
Main Shock ◽  
Central Italy ◽  
Strong Motion ◽  
Rupture Directivity ◽  
Time Data ◽  
Epicentral Area ◽  
Ground Shaking ◽  
Motion Data

In this paper we describe the performance of the ShakeMap software package and the fully automatic procedure, based on manually revised location and magnitude, during the main event of the Amatrice sequence with special emphasis to the M6 main shock, that struck central Italy on the 24th August 2016 at 1:36:32 UTC. Our results show that the procedure we developed in the last years, with real-time data exchange among those institutions acquiring strong motion data, allows to provide a faithful description of the ground motion experienced throughout a large region in and around the epicentral  area. The prompt availability of the rupture fault model, within three hours after the earthquake occurrence, provided a better descriptions of the level of strong ground motion throughout the affected area.  Progressive addition of  station data and  manual verification of the data insures improvements in the description of the experienced ground motions.  In particular, comparison between the MCS intensity shakemaps and preliminary field macroseismic reports show favourable similarities.  Finally the overall  spatial pattern of the ground motion of the main shock is consistent with reported rupture directivity toward NW and reduced levels of ground shaking toward SW probably linked to the peculiar source effects of the earthquake.

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.

The ShakeOut Earthquake Source and Ground Motion Simulations

2011 ◽  
Vol 27 (2) ◽  
pp. 273-291 ◽  
Author(s):  
Robert W. Graves ◽  
Brad T. Aagaard ◽  
Kenneth W. Hudnut
Keyword(s):  
Ground Motion ◽  
Ground Motions ◽  
Strong Motion ◽  
Peak Ground Velocity ◽  
Motion Modeling ◽  
Ground Acceleration ◽  
San Andreas ◽  
Basin Effects ◽  
Simulated Ground Motions ◽  
D Model

The ShakeOut Scenario is premised upon the detailed description of a hypothetical Mw 7.8 earthquake on the southern San Andreas Fault and the associated simulated ground motions. The main features of the scenario, such as its endpoints, magnitude, and gross slip distribution, were defined through expert opinion and incorporated information from many previous studies. Slip at smaller length scales, rupture speed, and rise time were constrained using empirical relationships and experience gained from previous strong-motion modeling. Using this rupture description and a 3-D model of the crust, broadband ground motions were computed over a large region of Southern California. The largest simulated peak ground acceleration (PGA) and peak ground velocity (PGV) generally range from 0.5 to 1.0 g and 100 to 250 cm/s, respectively, with the waveforms exhibiting strong directivity and basin effects. Use of a slip-predictable model results in a high static stress drop event and produces ground motions somewhat higher than median level predictions from NGA ground motion prediction equations (GMPEs).

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