Synthetic ground motions of the October 8, 2005 Kashmir earthquake (Mw 7.6): An inference to the site response and seismic hazard of Kashmir basin, NW Himalaya

2021 ◽  
pp. 3-12
Author(s):  
Hamid Sana
Keyword(s):  
Seismic Hazard ◽  
Site Response ◽  
Ground Motions ◽  
Nw Himalaya ◽  
Kashmir Earthquake ◽  
Kashmir Basin ◽  
2005 Kashmir Earthquake

Strain accumulation along various faults in the Kashmir Himalaya from InSAR

2021 ◽  
Author(s):  
Hamid Sana ◽  
Eric Fielding ◽  
Cunren Liang ◽  
Zhang Yunjun
Keyword(s):  
Time Series ◽  
Active Faults ◽  
Plate Boundary ◽  
Kashmir Himalaya ◽  
Kashmir Earthquake ◽  
The People ◽  
Kashmir Basin ◽  
2005 Kashmir Earthquake ◽  
Split Spectrum ◽  
Interferometric Sar

<p>We are using InSAR time-series analysis to measure the interseismic deformation across various faults of the Kashmir Himalaya. Active faults reaching the surface include the Main Boundary Faults, Bagh-Balakot Fault, which ruptured in the 2005 Kashmir earthquake (Mw 7.6), Jhelum Fault, Reasi Thrust and intra-Kashmir basin faults. We concentrate on these shallow faults that are closest to the people living in Kashmir. The Main Boundary Faults and other faults likely connect to the Main Himalayan Thrust (MHT) that is the plate-boundary megathrust beneath Kashmir and the rest of the Himalayas. The MHT has been suggested as a possible source for Mw 8 to Mw 8.5 earthquakes in this area. We have processed interferometric pairs from the Japan Aerospace Exploration Agency ALOS-2 L-band (24 cm wavelength) Synthetic Aperture Radar (SAR) wide-swath (ScanSAR) data acquired between 2015 and 2020. Initial interferometric SAR (InSAR) processing was carried out using the alos2App application of the InSAR Scientific Computing Environment (ISCE2) package, with ionospheric corrections enabled. We found that many scenes acquired in the winter form pairs that have low coherence due to snow cover in the High Himalayas and Pir Panjal Range. We also found that phase unwrapping in the mountains was improved by taking 10 range and 56 azimuth looks from the full-aperture ScanSAR for an effective resolution of about 200 meters. We are running a co-registered stack processing of the ALOS-2 SAR data, with self-consistent ionospheric corrections estimated using the split-spectrum method, using the new alosStack application of ISCE2 package to carry out time-series InSAR analysis, using an open-source Python toolbox, MIntPy.</p>

SEISMIC TIME-HISTORY GROUND-MOTIONS FOR A SPECIFIC SITE IN JAKARTA

2015 ◽  
Vol 77 (11) ◽  
Author(s):  
I Wayan Sengara ◽  
Muhammad Addifa Yulman ◽  
Andri Mulia
Keyword(s):  
Seismic Hazard ◽  
Linear Time ◽  
Site Response ◽  
Ground Motions ◽  
Ground Surface ◽  
Time History ◽  
Response Analysis ◽  
Building Collapse ◽  
Surface Development ◽  
Time Histories

Indonesia has developed new seismic building code based on risk-targeted ground-motions adopting 1 % probability of building collapse in 50 years. The new seismic design criterion, which is presented in the code, have combined both seismic hazard and building fragility. For performance-based analysis of high-rise buildings, a complex non-linear time-history analysis is needed. This paper presents results of study on development of the time-history with emphasing on procedure of developing pairs of time-history at ground surface for spesific site in Jakarta with reference to 2012 International Building Codes and ASCE-SEI-7-10. The study involves generation of time-history from reference base-rock through site-response analysis to ground surface. Development of time-history at ground surface with a procedure involving Square Root of the Sum of the Square method (SRSS) in order to reasonably scaled time-histories through spectral matching technique is presented herein. The matched time-histories are developed from various strong-motion records representing different earthquake sources dominant to control the site evaluated from de-aggregation within seismic hazard analysis. This work also adopts baseline corrections in which velocity and displacement components of matched time-histories can be drifted to zero at the end of recorded seismic time.

scholarly journals Reduction of Bias and Uncertainty in Regional Seismic Site Amplification Factors for Seismic Hazard and Risk Analysis

GeoHazards ◽  
2021 ◽  
Vol 2 (3) ◽  
pp. 277-301
Author(s):  
Mohammad Kamruzzaman Talukder ◽  
Philippe Rosset ◽  
Luc Chouinard
Keyword(s):  
North America ◽  
Seismic Hazard ◽  
Shear Wave ◽  
Site Response ◽  
Ground Motions ◽  
Site Amplification ◽  
Soil Profiles ◽  
Site Class ◽  
Amplification Factors ◽  
Wave Velocities

Site amplification factors in National Building Codes are typically specified as a function of the average shear wave velocity over the first 30 m (Vs30) or site class (A, B, C, D and E) for defined ranges of Vs30 and/or ranges of depth to bedrock. However, a single set of amplification factors may not be representative of site conditions across the country, introducing a bias in seismic hazard and seismic risk analyses. This is exemplified by significant differences in geological settings between East and West coast locations in North America. Western sites are typically characterized by lower impedance contrasts between recent surface deposits and bedrock in comparison to Eastern sites. In North America, site amplification factors have been derived from a combination of field data on ground motions recorded during West Coast earthquakes and numerical models of site responses that are meant to be representative of a wide variety of soil profiles and ground motions. The bias on amplifications and their impact on seismic hazards is investigated for the Montreal area, which ranks second for seismic risks in Canada in terms of population and hazard (PGA of 0.25 g for a 2475 years return period). Representative soil profiles at several locations in Montreal are analyzed with 1-D site response models for natural and synthetic ground motions scaled between 0.1 to 0.5 g. Since bedrock depths are typically shallow (<30 m) across the island, bedrock shear wave velocities have a significant influence on the impedance contrast and amplifications. Bedrock shear wave velocity is usually very variable due to the differences in rock formations, level of weathering and fracturing. The level of this uncertainty is shown to be greatly decreased when rock quality designation (RQD) data, common information when bore hole data are logged, is available since it is highly correlated with both shear and compression wave velocities. The results are used to derive region-specific site amplification factors as a function of both Vs30 and site fundamental frequency and compared to those of the National Building Code of Canada (2015). The results of the study indicate that there are large uncertainties associated with these parameters due to variability in soil profiles, soil properties and input seismic ground motions. Average and confidence intervals for the mean and for predictions of amplification factors are calculated for each site class to quantify this uncertainty. Amplifications normalized relative to class C are obtained by accounting for the correlation between site class amplifications for given ground motions. Non-linearity in the analysis of equivalent linear 1-D site response is taken into account by introducing the non-linear G/Gmax and damping ratios curves. In this method, it is assumed that the shear strain compatible shear modulus and damping ratio values remains constant throughout the duration of the seismic excitation. This assumption is not fully applicable to a case when loose saturated soil profile undergo heavy shaking (PGA > 0.3 g). In this study, all simulations with input motion PGA >0.3 g have been performed by using the EL method instead of the NL method considering that cohesive soils (clay and silt) at Montreal sites are stiff and cohesionless soils (sand and gravel) are considerably dense. In addition, the field and laboratory data required to perform NL analyses are not currently available and may be investigated in future works.

What is a reference site?

1996 ◽  
Vol 86 (6) ◽  
pp. 1733-1748 ◽  
Author(s):  
Jamison H. Steidl ◽  
Alexei G. Tumarkin ◽  
Ralph J. Archuleta
Keyword(s):  
Seismic Hazard ◽  
Ground Motion ◽  
Reference Site ◽  
Site Response ◽  
Ground Motions ◽  
Destructive Interference ◽  
Surface Rock ◽  
Reference Motion ◽  
Rock Site ◽  
A Site

Abstract Many methods for estimating site response compare ground motions at sites of interest to a nearby rock site that is considered a “reference” motion. The critical assumption in these methods is that the surface-rock-site record (reference) is equivalent to the input motion at the base of the soil layers. Data collected in this study show that surface-rock sites can have a site response of their own, which could lead to an underestimation of the seismic hazard when these sites are used as reference sites. Data were collected from local and regional earthquakes on digital recorders, both at the surface and in boreholes, at two rock sites and one basin site in the San Jacinto mountains, southern California. The two rock sites, Keenwild and Piñon Flat, are located on granitic bedrock of the southern California peninsular ranges batholith. The basin site, Garner Valley, is an ancestral lake bed with watersaturated sediments, on top of a section of decomposed granite, which overlies the competent bedrock. Ground motion is recorded simultaneously at the surface and in the bedrock at all three sites. When the surface-rock sites are used as the reference site, i.e., the surface-rock motion is used as the input to the basin, the computed amplification underestimates the actual amplification at the basin site for frequencies above 2 to 5 Hz. This underestimation, by a factor of 2 to 4 depending on frequency and site, results from the rock sites having a site response of their own above the 2-to 5-Hz frequencies. The near-surface weathering and cracking of the bedrock affects the recorded ground motions at frequencies of engineering interest, even at sites that appear to be located on competent crystalline rock. The bedrock borehole ground motion can be used as the reference motion, but the effect of the downgoing wave field and the resulting destructive interference must be considered. This destructive interference may produce pseudo-resonances in the spectral amplification estimates. If one is careful, the bedrock borehole ground motion can be considered a good reference site for seismic hazard analysis even at distances as large as 20 km from the soil site.

A subset of CyberShake ground-motion time series for response-history analysis

2021 ◽  
pp. 875529302098197
Author(s):  
Jack W Baker ◽  
Sanaz Rezaeian ◽  
Christine A Goulet ◽  
Nicolas Luco ◽  
Ganyu Teng
Keyword(s):  
Time Series ◽  
Los Angeles ◽  
Seismic Hazard ◽  
Ground Motion ◽  
Ground Motions ◽  
Response Spectra ◽  
Motion Time ◽  
History Analysis ◽  
Response History Analysis ◽  
Simulated Ground Motions

This manuscript describes a subset of CyberShake numerically simulated ground motions that were selected and vetted for use in engineering response-history analyses. Ground motions were selected that have seismological properties and response spectra representative of conditions in the Los Angeles area, based on disaggregation of seismic hazard. Ground motions were selected from millions of available time series and were reviewed to confirm their suitability for response-history analysis. The processes used to select the time series, the characteristics of the resulting data, and the provided documentation are described in this article. The resulting data and documentation are available electronically.

Sign in / Sign up

Export Citation Format

Share Document