scholarly journals Kathmandu Basin as a local modulator of seismic waves: 2D modelling of nonlinear site response under obliquely incident waves

2021 ◽  
Author(s):  
Elif Oral ◽  
Peyman Ayoubi ◽  
Jean-Paul Ampuero ◽  
Domniki Asimaki ◽  
Luis Bonilla
Keyword(s):  
Wave Propagation ◽  
Ground Motion ◽  
High Frequency ◽  
Site Response ◽  
Incidence Angle ◽  
Capital City ◽  
Seismic Behaviour ◽  
Soil Nonlinearity ◽  
Nonlinear Site Response ◽  
Basin Geometry

The 2015 Mw 7.8 Gorkha, Nepal earthquake is the largest event to have struck the capital city of Kathmandu in recent times. One of its surprising features was the frequency content of the recorded ground motion, exhibiting a notable amplification at low frequencies (< 2 Hz) and a contrasting depletion at higher frequencies. The latter has been partially attributed to the damper behaviour of the Kathmandu basin. While such weak high-frequency ground motion helped avoiding severe damage in the city, the catastrophic outcomes of earlier earthquakes in the region attest to a contrasting role of the Kathmandu basin as a broadband amplifier, in addition to possible source effects. Given the possibility of future strong events in the region, our main objective is to elucidate the seismic behaviour of the Kathmandu basin by focusing on site effects. We numerically model 2D P-SV wave propagation in a broad frequency band (up to 10 Hz), incorporating the most recent data for the Kathmandu basin geometry, soil stratigraphy and geotechnical soil properties, and accounting for the non-linear effect of multi-dimensional soil plasticity on wave propagation. We find that: 1) the Kathmandu basin generally amplifies low frequency ground motion (< 2 Hz); 2) waves with large incidence angles relative to vertical can dramatically amplify the high frequency ground motion with respect to bedrock despite the damping effect of soil nonlinearity; 3) the spatial distribution of peak ground motion amplitudes along the basin is highly sensitive to soil nonlinearity and wave incidence (angle and direction), favoring larger values near the basin edges located closer to the source, as observed during the 2015 event. Our modelling approach and findings can support the ongoing resilience practices in Nepal and can guide future seismic hazard assessment studies for other sites that feature similar complexities in basin geometry, soil stratigraphy and dynamic soil behaviour.

Kappa (κ) in the 2011 Great East Japan Earthquake

2020 ◽  
Vol 14 (06) ◽  
pp. 2050024
Author(s):  
Zhengru Tao ◽  
Xinyan Wang ◽  
Baihui Zhu ◽  
Tao Shang
Keyword(s):  
High Frequency ◽  
Site Response ◽  
Epicentral Distance ◽  
Soft Soil ◽  
Statistical Significance ◽  
Great East Japan Earthquake ◽  
Propagation Path ◽  
Data Sets ◽  
Borehole Data ◽  
Nonlinear Site Response

Kappa ([Formula: see text]) describes the amplitude decay of acceleration Fourier spectrum at high frequencies. Using the records of K-NET and KiK-net stations during the mainshock of the 2011 Great East Japan Earthquake, we examine if the typical measurement method of [Formula: see text] can be extended to this size of event and how propagation path and site condition affect [Formula: see text]. The strength of the linear relationship between epicentral distance and [Formula: see text] is the most apparent in the KiK-net borehole data; for other data sets, the statistical significance of the best-fitting logarithmic model is more tenuous. Our study on site effects reveals that high-frequency amplitudes diminish about 20% at soft soil stations than they do at hard rock stations. The effect on high-frequency filters is around diminution in most cases. And, the effect of nonlinear site response on [Formula: see text] values can be observed.

Seismic Wave Propagation and Basin Amplification in the Wasatch Front, Utah

2021 ◽  
Author(s):  
Morgan P. Moschetti ◽  
David Churchwell ◽  
Eric M. Thompson ◽  
John M. Rekoske ◽  
Emily Wolin ◽  
...  
Keyword(s):  
Wave Propagation ◽  
Ground Motion ◽  
Seismic Wave ◽  
Seismic Velocity ◽  
Site Response ◽  
Ground Motions ◽  
Seismic Wave Propagation ◽  
Velocity Models ◽  
Ground Motion Variability ◽  
Wasatch Front

Abstract Ground-motion analysis of more than 3000 records from 59 earthquakes, including records from the March 2020 Mw 5.7 Magna earthquake sequence, was carried out to investigate site response and basin amplification in the Wasatch Front, Utah. We compare ground motions with the Bayless and Abrahamson (2019; hereafter, BA18) ground-motion model (GMM) for Fourier amplitude spectra, which was developed on crustal earthquake records from California and other tectonically active regions. The Wasatch Front records show a significantly different near-source rate of distance attenuation than the BA18 model, which we attribute to differences in (apparent) geometric attenuation. Near-source residuals show a period dependence of this effect, with greater attenuation at shorter periods (T&lt;0.5  s) and a correlation between period and the distance over which the discrepancy manifests (∼20–50  km). We adjusted the recorded ground motions for these regional path effects and solved for station site terms using linear mixed-effects regressions, with groupings for events and stations. We analyzed basin amplification by comparing the site terms with the basin geometry and basin depths from two seismic-velocity models for the region. Sites over the deeper parts of the sedimentary basins are amplified by factors of 3–10, relative to sites with thin sedimentary cover, with greater amplification at longer periods (T≳1  s). Average ground-motion variability increases with period, and long-period variability exhibits a slight increase at the basin edges. These results indicate regional seismic wave propagation effects requiring further study, and potentially a regionalized GMM, as well as highlight basin amplification complexities that may be incorporated into seismic hazard assessments.

A Ground-Motion Prediction Model for Shallow Crustal Earthquakes in Greece

2020 ◽  
Author(s):  
David M. Boore ◽  
Jonathan P. Stewart ◽  
Andreas A. Skarlatoudis ◽  
Emel Seyhan ◽  
Basil Margaris ◽  
...  
Keyword(s):  
Prediction Model ◽  
Ground Motion ◽  
Site Response ◽  
Epistemic Uncertainty ◽  
Peak Ground Velocity ◽  
Motion Prediction ◽  
Ground Motion Prediction ◽  
Ground Acceleration ◽  
Magnitude Scaling ◽  
Nonlinear Site Response

ABSTRACT Using a recently completed database of uniformly processed strong-motion data recorded in Greece, we derive a ground-motion prediction model (GMPM) for horizontal-component peak ground velocity, peak ground acceleration, and 5% damped pseudoacceleration response spectra, at 105 periods ranging from 0.01 to 10 s. The equations were developed by modifying a global GMPM, to account for more rapid attenuation and weaker magnitude scaling in the Greek ground motions than in the global GMPM. Our GMPM is calibrated using the Greek data for distances up to 300 km, magnitudes from 4.0 to 7.0, and time-averaged 30 m shear-wave velocities from 150 to 1200  m/s. The GMPM has important attributes for hazard applications including magnitude scaling that extends the range of applicability to M 8.0 and nonlinear site response. These features are possible because they are well constrained by data in the global GMPM from which our model is derived. An interesting feature of the Greek data, also observed previously in studies of mid-magnitude events (6.1–6.5) in Italy, is that they are substantially overpredicted by the global GMPM, which may be a repeatable regional feature, but may also be influenced by soil–structure interaction. This bias is an important source of epistemic uncertainty that should be considered in hazard analysis.

Summary of the Abrahamson & Silva NGA Ground-Motion Relations

2008 ◽  
Vol 24 (1) ◽  
pp. 67-97 ◽  
Author(s):  
Norman Abrahamson ◽  
Walter Silva
Keyword(s):  
Standard Deviation ◽  
Ground Motion ◽  
Site Response ◽  
Hanging Wall ◽  
Site Location ◽  
Crustal Earthquakes ◽  
Nonlinear Site Response ◽  
Short Period ◽  
Standard Deviations ◽  
Improved Model

Empirical ground-motion models for the rotation-independent average horizontal component from shallow crustal earthquakes are derived using the PEER NGA database. The model is applicable to magnitudes 5–8.5, distances 0–200 km, and spectral periods of 0–10 sec. In place of generic site categories (soil and rock), the site is parameterized by average shear-wave velocity in the top 30 m ( VS30) and the depth to engineering rock (depth to VS=1000 m/s). In addition to magnitude and style-of-faulting, the source term is also dependent on the depth to top-of-rupture: for the same magnitude and rupture distance, buried ruptures lead to larger short-period ground motions than surface ruptures. The hanging-wall effect is included with an improved model that varies smoothly as a function of the source properties (M, dip, depth), and the site location. The standard deviation is magnitude dependent with smaller magnitudes leading to larger standard deviations. The short-period standard deviation model for soil sites is also distant-dependent due to nonlinear site response, with smaller standard deviations at short distances.

Ground Motion Prediction Equations for the Vertical Ground Motion Component Based on the NGA-W2 Database

2017 ◽  
Vol 33 (2) ◽  
pp. 499-528 ◽  
Author(s):  
Zeynep Gülerce ◽  
Ronnie Kamai ◽  
Norman A. Abrahamson ◽  
Walter J. Silva
Keyword(s):  
Ground Motion ◽  
Site Response ◽  
Vertical Component ◽  
Weighted Average ◽  
Motion Models ◽  
Nonlinear Site Response ◽  
Vertical Ground Motion ◽  
Vertical Ground ◽  
Standard Deviations ◽  
Ground Motion Models

Empirical ground motion models for the vertical component from shallow crustal earthquakes in active tectonic regions are derived using the PEER NGA-West2 database. The model is applicable to magnitudes 3.0–8.0, distances of 0–300 km, and spectral periods of 0–10 s. The model input parameters are the same as used by Abrahamson et al. (2014) except that the nonlinear site response and depth to bedrock effects are evaluated but found to be insignificant. Regional differences in large distance attenuation and site amplification scaling between California, Japan, China, Taiwan, Italy, and the Middle East are included. Scaling for the hanging-wall effect is incorporated using the constraints from numerical simulations by Donahue and Abrahamson (2014) . The standard deviation is magnitude dependent with smaller magnitudes leading to larger standard deviations at short periods but smaller standard deviations at long periods. The vertical ground motion model developed in this study can be paired with the horizontal component model proposed by Abrahamson et al. (2014) to produce a V/H ratio. For applications where the horizontal spectrum is derived from the weighted average of several horizontal ground motion models, a V/H model derived directly from the V/H data (such as Gülerce and Abrahamson 2011 ) should be preferred.

scholarly journals Developing a model for the prediction of ground motions due to earthquakes in the Groningen gas field

2017 ◽  
Vol 96 (5) ◽  
pp. s203-s213 ◽  
Author(s):  
Julian J. Bommer ◽  
Bernard Dost ◽  
Benjamin Edwards ◽  
Pauline P. Kruiver ◽  
Michail Ntinalexis ◽  
...  
Keyword(s):  
Ground Motion ◽  
Site Response ◽  
Ground Motions ◽  
Essential Element ◽  
Mitigation Measures ◽  
Gas Field ◽  
Near Surface ◽  
Nonlinear Site Response ◽  
Wide Range ◽  
Groningen Gas Field

AbstractMajor efforts are being undertaken to quantify seismic hazard and risk due to production-induced earthquakes in the Groningen gas field as the basis for rational decision-making about mitigation measures. An essential element is a model to estimate surface ground motions expected at any location for each earthquake originating within the gas reservoir. Taking advantage of the excellent geological and geophysical characterisation of the field and a growing database of ground-motion recordings, models have been developed for predicting response spectral accelerations, peak ground velocity and ground-motion durations for a wide range of magnitudes. The models reflect the unique source and travel path characteristics of the Groningen earthquakes, and account for the inevitable uncertainty in extrapolating from the small observed magnitudes to potential larger events. The predictions of ground-motion amplitudes include the effects of nonlinear site response of the relatively soft near-surface deposits throughout the field.

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