National Earthquake Hazards Reduction Program Research Articles

Seismic Risk Assessment of Built Environment in the Himalayan Foothill City of Dehradun, Uttarakhand

Himalayan foothill city of Dehradun in Uttarakhand state is located in a tectonically active region and is prone to earthquakes. The growth of Dehradun city is analysed using high resolution remote sensing datasets in the current study, with a focus on its vulnerability to seismic risks for single and double storey structures as the city is predominantly made up of low-rise structures. Analysis shows that 10% of urban expansion has occurred in spectral acceleration zones that are vulnerable to double-storey buildings, while 38% of urban expansion has happened in spectral acceleration zones that are vulnerable to single-storey buildings. The proposed land use as per Dehradun Masterplan 2041 is examined with reference to National Earthquake Hazards Reduction Program (NEHRP) for seismic regulating provisions. It is emphasized that the intended land use is incongruous in areas with higher spectral acceleration zones since it comprises structures with higher occupancy and the amenities required during post-earthquake rehabilitation. On the other hand, the open spaces are more appropriate in these locations, which will lessen susceptibility as the influence of seismic forces can be sufficiently attenuated. The present study, thus highlights the significance of including seismic risk information in urban planning processes in order to ensure resilient cities.

Stochastic assessment of 3‐D tunnels in near‐fault ground motion using modified domain reduction method

AbstractA robust assessment of tunnels due to uncertainties present in soil and ground motion properties can affect the dynamic response of these structures. In this paper, a stochastic analysis considering an aleatory variability in shear velocity Vs by performing Monte Carlo simulations and assessing its influence on underground tunnels. To numerically assess the response of the soil‐tunnel system to near‐fault earthquake ground motion, the required computational domain usually spans multiple kilometers including both earthquake fault and the structure. Thus, these simulations are computationally expensive. An efficient alternative method, that is, the Domain Reduction Method (DRM), in which a modular two‐step methodology for reducing the computational costs in the large domain analysis is employed. A 3‐D soil‐tunnel structure interaction is modeled to simulate the response of tunnel subjected to an inclined earthquake fault. The numerical simulation of the soil‐tunnel‐fault system is conducted in an open‐source FE package called Multi‐hazard Analysis for STOchastic time DOmaiN phenomena (MASTODON) based on MOOSE framework. The interactive analyses are carried out for three distinct types of soils based on National Earthquake Hazards Reduction Program (NEHRP) provision, that is, soft, medium, and hard, by generating 130 realizations. The results provide many insights into the influence of local site effects, that is, frequency shift for the peak response and the importance of input ground motion characteristics that govern the response of underground structures. The dynamic response of the structure is very sensitive to the uncertainty in rock material properties, especially, the stiffness of the rock sample and the shear wave velocity.

Physico-mechanical Properties Estimation of Upper Siwalik Sandstone using Field (MASW) and Laboratory Test, Himachal Himalaya, India

Abstract A study on the Upper Siwalik Sandstone was conducted to determine and compare the relationship between shear wave velocity and the petro-physical and petro-mechanical characteristics of the sandstone. Two localities in the Himachal Himalaya’s Bilaspur district were sampled for collection of sandstone of Upper Siwalik. The method of Multichannel Analysis of Surface Waves (MASW) was used to obtain average shear wave velocity at 30m depth (Vs30) in the field. The shear modulus of rocks is intimately correlated with the Vs30 parameter. The Vs30 value is 185 m/s for the Majher Khad (sandstone A) region and 366 m/s for the Dharot region (sandstone B). Based on obtained Vs30 values these two regions are classified under class D and class C respectively by the National Earthquake Hazards Reduction Program (NEHRP). Both the rocks belong to Upper Siwalik Sandstone, but diversity in Vs30 and shear modulus values can be ascribed to the composition of minerals, the size of the grains, and the cementing substances present in the rock.

An equivalent point-source stochastic model of the NGA-East ground-motion models

The main objective of this study is to estimate seismological parameters in Central and Eastern North America (CENA), including the geometrical spreading, anelastic attenuation, stress parameter, and site attenuation parameters. In this study, we use particle swarm optimization (PSO) to invert a weighted average of the median 5%-damped pseudo-spectral acceleration (PSA) predicted from the Next Generation Attenuation-East (NGA-East) ground-motion models (GMMs) to develop a point-source stochastic GMM with a well-constrained set of ground-motion parameters. Magnitude-specific inversions are performed for moment magnitude ranges M = 4.0–8.0, rupture distances Rrup = 1–1000 km, and periods T = 0.01–10 s, and National Earthquake Hazard Reduction Program site class A conditions. The result of this study yields a single stochastic GMM that yields PSA values similar to the median NGA-East GMMs. The parameters derived from this study can be used for the hybrid empirical method (HEM) applications. This study is the first to perform a formal inversion using the GMMs developed for the NGA-East project. The approach has been validated using simulated small-to-moderate magnitude and large-magnitude data derived from the NGA-West2 GMMs.

Seismic site characterization using MASW and correlation study between shear wave velocity and SPT[sbnd

A seismic site characterization study is carried out in the south of the foothills of tectonically active Himalayan region. During an earthquake, the dynamic characteristics of the shallow subsurface strata can influence seismic shaking in the region, causing damage to civil infrastructures. The seismic site characterization study with shear wave velocity (Vs) is performed using the Multi-channel Analysis of Surface Wave (MASW) technique, which is particularly challenging to implement in the densely inhabited areas. However, the standard penetration test (SPTN) commonly measured by civil engineers can be utilized to compute Vs of such areas by establishing a correlation between Vs and the SPT-N values.In the study area, MASW data were acquired at twelve different locations, whereas SPT-N tests were available from 26 boreholes. Twelve borehole locations closer to the MASW survey lines were paired to establish relationships between SPT-N and Vs. The developed linear and non-linear correlation functions were found to be statistically similar. Furthermore, the linear correlation function is used for estimating Vs from SPT-N in remaining 14 boreholes. The new correlation functions were further compared with previously reported empirical relationships from other areas. The current relationship can be used for geoengineering purposes at different sites with similar geological conditions.Shear wave velocity derived from the MASW surveys and estimated from the new empirical relationship was utilized for seismic site characterization based on average shear wave velocity up to 30 m depth (Vs30). The Vs30 map of the study site is prepared and classified in accordance with the National Earthquake Hazard Reduction Program (NEHRP-2020). The calculated Vs30 value of the study site ranges from 285 to 375 m/s. The major portion of the study area lies under Site Class CD, with a minor portion under Site Class D. In the event of an earthquake, some zones can potentially have stronger ground amplification, particularly in Site Class D and may have damaging effects. A series of average shear wave velocity maps for different depths are prepared to help geotechnical engineers in identifying and mitigating geotechnical risks. Furthermore, there are potential geohazard risks as certain depths show low shear velocity.

Seismic site classification of Nakhon Nayok City, central Thailand, using the MASW technique

Shear-wave velocity (Vs) of soils in Nakhon Nayok City, Central Thailand were determined using the Multi-Channel Analysis of Surface Wave technique. The Vs. of 35 tested sites were weighted average to 30 m depth based on the National Earthquake Hazards Reduction Program (NEHRP) criteria, which revealed NEHRP site classes C, D, and E within the study area. Soil class C was found in the north of the city. Moreover, most of the residential area of Nakhon Nayok City is positioned on soil classes D and E. The soil in the area of study has an amplification value ranging from 1.4 to 3.9. The central and southwestern parts of the city, which mainly consist of soft sediments, have a higher amplification value than that in the northern part, which mainly consists of coarse grain soils of colluvial deposits. Based on the NEHRP and amplification value, the Nakhon Nayok City area will experience some effect from ground shaking from nearby and far away earthquake seismic sources.

Stochastic finite fault modeling of Mw 6.4 earthquake along Indo-Burmese arc and site classification of its seismic recording station

This study simulates the strong ground motion of an earthquake having magnitude 6.4 occurred on 4 February 2011 in Indo-Burmese Arc (IBA). This earthquake recorded on seven seismic recording stations namely Jowai, Jorhat, Sibsagar, Nagaon, Guwahati, Cooch Bihar and Kokhrajhar. Also, estimation of site class performed to observe the site effects of recording stations in this study. The simulation performed on the basis of revised stochastic finite fault model with dynamic corner frequency and site class for the seismic recording station where the earthquake recorded has been estimated by using Horizontal to Vertical Spectral Ratio (HVSR) technique because modeling and simulation of ground motion majorly depend upon the recorded ground motion as well as site effects, where earthquake has been recorded. The revised well known finite source simulation program (EXSIM) used in this study becomes efficient in providing the results for small magnitude earthquake occurred at large distance. The average HVSR curves plotted for all the recording stations, providing peak frequency for all 7 sites. It is observed from the present work that simulated time histories as far as primary attributes, for example, Fourier spectra, Peak ground acceleration (PGA), Response spectra, Predominant frequency are in close concurrence with the recorded ones. The predominant frequency (fpeak) obtained from HVSR technique has been validated from existing literature for the estimation of site class for seismic recording stations. The fpeak determines the average shear wave velocity (Vs30) at depth of 30 ​m of overburden thickness which varies from 200 ​m/s to 1600 ​m/s according to Program for Excellence in Strong Motion Studies (PESMOS). Whereas, National Earthquake Hazard Reduction Program (NEHRP) provision consider the site class for Vs30 below 180 ​m/s. Due its wide range of site characterization, it has been adopted globally. Therefore, in this study, the site class obtained has been compared with the site classification scheme recommended by PESMOS, NEHRP provisions and previous literature. However, the ground motion parameters and the soil classification of the earthquake recording stations for the IBA region has not been explored yet even after seeing its severity in the past decades. Productive representation of present earthquake gives the confidence to understand and evaluate seismic danger at various parts of Indo- Burmese region from tremors of various sizes. In this study it is proposed that PESMOS site classification data should be revised because it covers wide range of soil types just into three (A, B and C type) class.

Seismic Performance of Special Truss Moment Frames With X-Bracing Type: Influence of Building Height

Abstract This study investigated the implementation of Special Truss Moment Frames (STMF) X-braced type in accordance with the recommendations of the National Earthquake Hazards Reduction Program (NEHRP), 1997:2000 and Indonesian National Standards (SNI) 1726 where it is stated that the STMF may only be used up to a maximum building height of 48 m (160 feet) for Seismic Design Category of D. The analyses compared the seismic response of apartment buildings using STMF system with different height: 44 m (11 stories), 48 m (12 stories), and 52 m (13 stories). The nonlinear behaviors were investigated through a series of nonlinear time history and pushover analyses, including the inelastic response of the structural components, top-roof displacement, drift ratio, and ductility. The structural modeling and the selection of steel sections were performed in SAP 2000 based on SNI 1726 code, considering that the structure was built on medium soil in Aceh region. Seismic performance was examined through a series of pushover and nonlinear time history analysis (NLTHA) using three scaled accelerogram: Elcentro 1940, Northridge 1994 and Kobe 1995 records. The results of the study show that in case of STMF structure with the height of 52 m (higher than the maximum height of STMF structure stated in the codes), the seismic performance of the structure was excellent and met the requirements. Axial plasticization occurred only in X-braces, not followed by the formation of plastic hinges at the ends of the ductile segments. Meanwhile, the other structural components remained elastic. This indicates that the structure can still be used after the earthquake, by replacing only the X-braced components. The drift ratio met the requirements and the roof displacements behavior was asymptotic, indicating that there is no residual horizontal displacement of the building after the seismic loads occurred.

Investigation of Road Pavement Failures Using Active and Passive Surface Wave Methods in Parts of Calabar Municipality, Cross River State, Nigeria

The active and the passive techniques of surface wave were employed to investigate some major road pavement failures within the Calabar metropolis, Cross River State. The dispersion curves from MASW (active) and ReMi (passive) were inverted to give a 1D shear wave velocity model. The aim of this study was to comparatively investigate the major causes of the incessant road pavement failures especially few months after its construction and repairs within the study area using the shear wave velocity and blow count (N values). These roads are all located within the same geologic setting of the Calabar Coastal Plan Sand and showed evidence of road failures ranging from pot holes, alligator cracking, rutting and shear failure cracking etc. For each site, two sets of data were collected; the Passive and the Active seismic surface wave data. The survey was able to gather the following data from each location; shear wave velocity, primary wave velocity, N-values for both the active and the passive data which were both derived by the Seisimager surface wave software. The software was used to delineate low velocity layers within the depth of 4m – 6m at the failed portions of the survey sites exception of location 1 (the control site) which showed an ideal situation of increasing velocity with depth. These low velocity layers were inferred to be the major cause of the incessant failure of the pavements in the survey areas. These velocities and the N- values (blow count) were used to classify each location into sites C, D and E, according to the 1997 National Earthquake Hazards Reduction Program (NEHRP).

Amplification analysis at Nador city and surrounding area (NE of Morocco)

This study presents a ground response assessment performed at Nador city (Morocco) and surrounding areas. We carried out the one-dimensional equivalent linear approach using the known geotechnical parameters to derive amplification analysis at studied sites, using the shear wave velocity (VS(30)) derived from boreholes. Seismic hazard assessment is performed using two gridded seismicity models and four ground motions attenuation equations, in order to address the epistemic uncertainty in a logic-tree framework. Seismic hazard maps depicting the mean estimated hazard values and including the uncertainty are presented in terms of spectral acceleration at 0.0, 0.1 and 0.2 s, with 10% and 5% probabilities of exceedance in 50 years, and for B, B/C and C soil conditions, as defined by the National Earthquake Hazards Reduction Program classification and for local site conditions as well. Typical values of Peak Ground Acceleration (PGA) equal to 0.18g±0.03 and 0.26g±0.05 are obtained at the Nador city for 475 and 975 return period respectively and for B/C soil conditions. The deaggregation analysis for both returns periods (475 and 975 years) in terms of magnitude-distance (named 2D deaggregation) and in azimuth (longitude and latitude named 3D deaggregation) allows us to derive the contribution of the different couple of magnitude-distance (M,D) and the different sources, the controlling earthquake are also determined at the five considered cities, for both return periods. From the site-specific seismic hazard analysis performed at five main cities located in the studied area, the seismic hazard curves and the uniform hazard spectra (UHS) are obtained with their uncertainties for the considered return periods and soil conditions, as well as the design spectra proposed by Malhotra (2005). Real accelerogram time-history is used to generate compatible acceleration time-history with the design spectra proposed by Malhotra (2005) and the EC-8 type 2 (Eurocode 8.2004), for both return periods and for B/C soil conditions. The lower root mean square error value (RMSE) is archived by using the Malhotra design spectra for the considered return periods. The results display a clear amplification in silty and clayey soils, greater than in silt-gravely soils, as well as no significant amplification in volcanic soils. Moreover, the resulting fundamental frequency is in the range of 1.4–2.8 Hz, and the maximum amplification factor observed in Nador is about 3.5. These values are consistent with the results derived from ambient noise, seismic records using HVSR technique and with the values given by Moroccan Seismic Code in the 2000 and 2011 regulations.

Site effect estimation for shallow engineering bedrock using microtremor HVSR method and geotechnical borehole data, Riyadh city, Saudi Arabia

The estimation of local site response and geotechnical properties of near-surface deposits becomes essential for improving the building codes especially in big cities as Riyadh. This study aims to estimate the site response parameters in the northern expansion zone of Riyadh city. Microtremor measurements were recorded at 45 sites at the study area, north of Riyadh, and the resonance frequency and amplification factor were calculated using the H/V spectral ratio approach. The microtremor data has been processed using geopsy software to get the H/V curve and get the value of the resonance frequency (fo) and amplitude (Ao). The values of the resonance frequency span from 0.79 to 45 Hz, while the amplification factor ranges from 1.22 to 8.5, indicating the presence of foundation bedrocks at various levels with varying soil thickness. Moreover, the N60 parameter was calculated to correct the SPT-N uncorrected field readings in order to estimate the shear wave velocity parameter down to 30 m depth (Vs30). The computed shear wave velocity for a depth of 30 m (Vs30) ranges from 210 to 630 m/s. Accordingly, the soil at the studied area can be divided into two site soil classes C and D according to the National Earthquake Hazard Reduction Program (NEHRP). The findings of this study should be considered as part of the development of the Saudi Building Code for Riyadh City.

Correlation between SPT-N and shear wave velocity (VS) and seismic site classification for Amaravati city, India

The present study proposes a set of correlations between standard penetration number (SPT-N) and shear wave velocity (VS) using nonlinear regression analysis. These correlations have been developed for different categories of soil for Amaravati city. This study area is the current de facto seat of government of the Indian state of Andhra Pradesh, India. For this study, SPT-N data has been obtained from 400 boreholes distributed across the city of area 217.23 km2. Most of the boreholes considered for this study have a boring depth of 25 m to 45 m below the recorded ground surface. A comparison between the proposed correlations with existing worldwide accepted correlations has been performed to check the authenticity of this study. In addition to this, Vs obtained from the recommended correlations have been validated with the Vs obtained from 30 microtremor tests as well as established graphical methods. Furthermore, the seismic site classification of the study area has been conducted using the developed correlation for all soils. It is observed that the major part of Amaravati city falls under class D as per the National Earthquake Hazard Reduction Program (NEHRP) provisions. The average SPT-N and VS distribution across the city has also been generated at depths of 5, 10, 15, 20, 25, and 30 m. The outcomes of the study can be further used for the design of earthquake-resistant structures, seismic hazard studies, estimation of ground movements, and generation of site-specific synthetic ground motions.

Characteristics of the foundation rocks using geophysical techniques: A case study for the Egyptian solar plant site, Aswan, Egypt

The main target of the present study is to investigate the foundation layers and the subsurface structures in an Egyptian solar plant site using geophysical techniques including the seismic refraction and Multichannel Analysis of Surface Waves (MASW). The studied solar park is situated at about 40 km to the north of Aswan city on the Aswan-Cairo highway road and is classified as the largest solar plant in Africa and worldwide. Due to its location in the vicinity of the most prone earthquake area in Egypt (Aswan seismic zone); it is imperative to mitigate the earthquake hazard in this region. The geophysical results show that the subsurface foundation in this site is primarily composed of two layers. The upper one is loose and incompetent soil sediments that extend down to about 10 m depth with P-wave velocity ranging from 400 to 1000 m/s and shear-wave velocity ranging from 260 to 550 m/s. The deeper section is considered the main foundation layer with velocities ranging between 650 and 1900 m/s and from 350 to 950 m/s for P-wave and shear-wave, respectively. The average shear-wave velocities calculated for the topmost 30 m (Vs30) vary almost between 319 and 834 m/s; thereby the studied site is primarily ranked into classes C&D (180-360 m/s & 360-760 m/s, respectively) according to the National Earthquake Hazards Reduction Program (NEHRP) soil classification. Additionally, the southwestern and southeastern zones of the site area are characterized by maximum velocity values, relative high values of rock densities, rigidity or shear modulus “μ”, Standard Penetration Test (N-Value), ultimate bearing capacity and allowable bearing capacity, while the low values are observed through the northern and middle sectors across the area. This study an integral part of many works being carried out delineating the subsurface foundation structures around the solar plant and allows the most appropriate sites for constructing the renewable energy plants to be sited away from the highly hazards prone areas.

A New Model for Vertical-to-Horizontal Response Spectral Ratios for Central and Eastern North America

ABSTRACT It is a well-known fact that critical structures are required to be designed for the vertical effects of earthquake ground motions as well as the horizontal effects. We developed a new model for the spectral ratio of vertical-to-horizontal components of earthquakes (V/H ratio) for central and eastern North America (CENA). The proposed V/H ratio model has the advantage of considering the earthquake magnitude, source-to-site distance, and the shear-wave velocity of soil deposits in the upper 30 m of the site for peak ground acceleration and a wide range of spectral periods (0.01–10.0 s). The model evaluation is based on a comprehensive set of regression analysis of the compiled Next Generation Attenuation-East database of the available CENA recordings with M ≥ 3.4 and Rrup<1000 km. The median value of the geometric mean of the orthogonal horizontal motions rotated through all possible nonredundant rotation angles, known as the RotD50, is used along with the vertical component to perform regression using the nonlinear mixed-effect regression. We excluded the earthquakes and recording stations in the Gulf Coast region due to their different ground motion attenuation (Dreiling et al., 2014). To compute V/H ratios for the Gulf Coast region, we refer the readers to the study of Haji-Soltani et al. (2017). Moreover, we excluded the National Earthquake Hazard Reduction Program site class E sites from consideration because of their complex site response characteristics and their potential for nonlinear site effects. The predicted V/H ratios from the proposed model are compared with recently published V/H ratio models. We suggest our model to be used for developing the vertical response spectra for CENA sites.

Site classification of seismic recording stations of Garhwal region of earthquake early warning system for Uttarakhand, India

Site classification is vital to carry out seismic hazard analysis of a region and get the damage patterns caused by earthquakes. In the present study, the ground motion of earthquakes recorded from 2015 to 2019 at 84 sites of the seismic network array of Earthquake Early Warning System for Uttarakhand are analyzed for site classification purposes. The predominant period from the mean horizontal to vertical spectral ratio curves was estimated. The classification schemes devised by Japan Road Association and National Earthquake Hazards Reduction Program are applied to classify the sites. Along with this, two other site classification indexes schemes are also applied for classification purposes. Data winnowing techniques are used over the ground motion records to pick out desirable quality records. Conclusively, the site class with the highest recurrence rate amongst the used methods is selected as the final class for that particular site. The effect of magnitude, distance and depth on horizontal to vertical spectral ratio are described and concluded that these factors do not significantly affect the ratio curves. The average horizontal to vertical spectral ratio curves obtained for all the sites matches well with the existing literature. The classification of a few sites are verified from the classification done by other methods in recent studies. It is evident from the results that the classification done in this study matches well with them.

Soil Profile Database and Site Classification for National Strong-Motion Stations in Western China

Abstract As part of a broader effort to develop ground-motion data resources for China in a manner consistent with Next Generation Attenuation projects, we develop a database of geotechnical soil profiles and shear-wave velocity (VS) logs for sites having ground-motion accelerometers (this database is referred to as soil profile database [SPD]), and then use that data to develop site parameters. The site information is compiled for stations within the National Strong Motion Observation Network System (NSMONS) of China. This effort is focused on four provinces in western China (Yunnan, Sichuan, Gansu, and Xinjiang), which contribute 871 of 2023 NSMONS stations throughout China. Of the 871 sites, the SPD provides site information for 678 sites, or 78% of the total. To develop the SPD, geotechnical logs and/or VS profiles are compiled for 637 sites. This information is derived from previously unpublished reports and is assembled here in a uniform format and partially disseminated (only approximate site locations are provided). The remaining 41 sites in the SPD have confirmed bedrock conditions at the ground surface. Site metadata and parameters are compiled into a database, included as a supplemental material to this article, that includes the depth to the first occurrence of 0.5 km/s shear-wave velocity (Z0.5), three time-averaged shear-wave velocity parameters (VSe, VS20, VS30), and site classifications based on the Chinese building seismic design code and National Earthquake Hazards Reduction Program Provisions. For sites with VS profiles that do not extend to 30 m, we present region-specific recommendations for extrapolating time-averaged velocities from the profile depth to 30 m. For sites with geotechnical logs but no profiles, we present procedures to estimate VS profiles from which the earlier parameters can be derived.

Influence of Masonry Infill on Seismic Design Factors of Reinforced-Concrete Buildings

Infill walls are the most common separator panels in typical reinforced-concrete (RC) frame structures. It is crucial to investigate the influence of the infill walls on the earthquake behavior of RC frames. The load resistance of infill materials was often not taken into account in the designing phase, whereas the infill walls have significant contributions to the structural behavior under lateral and vertical loadings. A three-dimensional 4-story RC building is designed, and in order to make a realistic model, different infill walls configurations were taken into account with the openings in the infill. Four different models were created for structural analysis for infill wall effects, namely, full RC infilled frame (Model I), corner infill at ground story RC infilled frame (Model II), open ground story RC infilled frame (Model III), and bare RC frame (Model IV). Static adaptive pushover analysis has been performed for all structural models by using the SeismoStruct software. The double strut nonlinear cyclic model was used for modeling the infill walls. In this study, three different compressive strengths of infill walls are taken into consideration, and the effects on seismic design factors (namely, the response reduction factor, the ductility, the overstrength factor, and the deflection factor) are calculated. The obtained values of the response reduction factor (R) are compared with the given values in the BIS code. The results show that the R factors of all RC infilled frames are decreased when the compressive strength of the masonry infill reduces. However, the R values of bare frames are less than the corresponding values recommended in the BIS code. It is worth noting that the National Earthquake Hazards Reduction Program (NEHRP) provisions underestimate the deflection factors of the reinforced-concrete (RC) frames according to the evaluated deflection factors of the herein studied RC frames.

Imaging subsurface geological complexity (2D/3D) beneath the Greater Srinagar region of the Kashmir basin, Northwest Himalaya

ABSTRACTA high‐resolution microtremor measurement in Greater Srinagar city of the Kashmir valley has been analysed to image 2D and 3D subsurface geological complexities. This region is located in the highly seismogenic Himalayan belt and sits atop a deep sedimentary lake bed with a laterally varying thickness of soft sediments. Srinagar region is a major economic centre and the capital city of the Kashmir valley with 2 million inhabitants living at high seismic risk. To assess the subsurface complexity beneath the city, we present: (1) high‐resolution subsurface shear wave velocity Vs structure using the horizontal‐to‐vertical spectral ratio inversion; (2) shear wave velocity for top 30 metres of soil column (VS30) map with National Earthquake Hazards Reduction Program site classification; (3) comparison of VS30 maps calculated from horizontal‐to‐vertical spectral ratio inversion and topographic slope methods; and (4) azimuthal behaviour of horizontal‐to‐vertical spectral ratio peaks, all of which unravel the subsurface spatial heterogeneity and suitability for the building of engineering structures in the study area. In addition, a new matlab code is applied to generate 3D subsurface Vs slices in the study region in different directions using its pre‐generated 2D Vs profile data. The presented potentiality of microtremor horizontal‐to‐vertical spectral ratio technique in Srinagar region, which lies on the eastern edge of the basin with significant topographic irregularities, indicates an uneven distribution of local site effects (primary and secondary) in the case of strong ground motion. The comprehensive results can be promising in engineering analyses of local ground and structural responses in order to mitigate the impact of earthquake occurrence and seismic risk in the city and adjoining regions.

Ground motion models for shallow crustal and deep earthquakes in Hawaii and analyses of the 2018 M 6.9 Kalapana sequence

The damaging 4 May 2018 M 6.9 Kalapana earthquake and its aftershocks have provided the largest suite of strong motion records ever produced for an earthquake sequence in Hawaii exceeding the number of records obtained in the deep 2006 M 6.7 Kiholo Bay earthquake. These records provided the best opportunity to understand the processes of strong ground shaking in Hawaii from shallow crustal (< 20 km) earthquakes. There were four foreshocks and more than 100 aftershocks of M 4.0 and greater recorded by the seismic stations. The mainshock produced only a modest horizontal peak ground acceleration (PGA) of 0.24 g at an epicentral distance of 21.5 km. In this study, we evaluated the 2018 strong motion data as well as previously recorded shallow crustal earthquakes on the Big Island. There are still insufficient strong motion data to develop an empirical ground motion model (GMM) and so we developed a GMM using the stochastic numerical modeling approach similar to what we had done for deep Hawaiian (>20 km) earthquakes. To provide inputs into the stochastic model, we performed an inversion to estimate kappa, stress drops, Ro, and Q(f) using the shallow crustal earthquake database. The GMM is valid from M 4.0 to 8.0 and at Joyner–Boore (RJB) distances up to 400 km. Models were developed for eight VS30 (time-averaged shear-wave velocity in the top 30 m) values corresponding to the National Earthquake Hazards Reduction Program (NEHRP) site bins: A (1500 m/s), B (1080 m/s), B/C (760 m/s), C (530 m/s), C/D (365 m/s), D (260 m/s), D/E (185 m/s), and E (150 m/s). The GMM is for PGA, peak horizontal ground velocity (PGV), and 5%-damped pseudo-spectral acceleration (SA) at 26 periods from 0.01 to 10 s. In addition, we updated our GMM for deep earthquakes (>20 km) to include the same NEHRP site bins using the same approach for the crustal earthquake GMM.

Geotechnical zonation and soil–structure interaction at Puerto Vallarta, México

We performed a seismic vulnerability assessment that involves geotechnical and building structure analysis for Puerto Vallarta, Mexico, a city located along the pacific coast. Puerto Vallarta, like many other Latin American cities, has significant seismic risk. We implemented the multichannel analysis of surface waves and the horizontal-to-vertical spectral ratio methods to estimate shear wave velocity and soil resonance frequency. We considered a standard penetration test to determine the penetration resistance and soil classification. We divided the Puerto Vallarta into four zones according to a building taxonomy based on construction materials and structural systems and story number and height. The VS30 parameter shows that Puerto Vallarta has soil types C, D, and E according to the National Earthquake Hazard Reduction Program (NEHRP). We classified the soil into three types based on the estimated fundamental period, TS. Both VS30 and TS parameters showed an overall transition of soil properties from the mountain toward the valley area. The standard penetration tests corroborate the results of the implemented geophysical methods. The correlation between the fundamental period of the soil and the fundamental period of the most common building types at each zone of Puerto Vallarta indicates high seismic vulnerability. We identify building vulnerability to resonance effects principally at the south and along the coast of the Puerto Vallarta. This work combines academic and governmental efforts to solve a real and transcendental problem since it might directly affect the regulation and evaluations of structures in the area.