Hard Rock Sites Research Articles

Spatial coherency analysis of seismic motions from a hard rock site dense array in Busan, Korea

Spatial coherency analysis of seismic motions from a hard rock site dense array in Busan, Korea

Study on the coupling effects between reactor coolant system and the internal structure on floor response spectrum of small modular reactor

AbstractAccording to Chinese code and US standard review plan (US SRP), when the equipment and structure satisfy certain decoupling conditions, the seismic analysis of the structure is performed using a decoupling method, where only the mass of the equipment is considered in the structure. The reactor coolant system of small modular reactor (SMR) which is integrated is different from that of PWR, and it is more likely to affect the seismic response of the supporting structure. In this paper, a decoupling model was first constructed based on the decoupling principles in the code. Then, a coupled model is built by connecting the main loop system model with the structure. The floor response spectra of the decoupling model and the coupled model are analyzed separately using ACS SASSI software to investigate the coupling effect. By the comparison of the results, the preliminary conclusions are drawn as follows: the decoupling criteria in code are met for the internal structure and reactor coolant system. For hard rock site, the coupling effect has negligible influence on the in‐structure response spectra (ISRS) for most of the structure except the reactor pit, which shows obvious change in the high‐frequency region. For soft soil site, there is no remarkable influence on the ISRS of the structure even for the reactor pit due to the filter effect of the site to the high‐frequency component in the seismic input. For the site with shear wave velocity greater than 1100 m/s, the influence of couple effect cannot be ignored.

Seismological Ground-Motion Models for Generic Hard-Rock Site Condition in Western Canada

ABSTRACT We develop ground-motion models (GMMs) to characterize the Fourier amplitude spectrum (FAS) for earthquakes in British Columbia (B.C.), Canada. GMMs developed for FAS are useful for understanding the underlying seismological parameters and can be transformed into GMMs for response spectral values for other applications (e.g., probabilistic seismic hazard analysis [PSHA]). The GMMs are calibrated using a compiled FAS database, referenced to a B.C. generic hard-rock site condition (shear-wave velocity ∼2285 m/s). The GMMs are developed separately for crustal, in-slab, transition, offshore, and Haida Gwaii events. The GMMs are calibrated using data mostly from M 2.5 to 5.5 earthquakes recorded at rupture distances of ∼50 to 500 km. Outside this range, the models are constrained by a seismological model supplemented with sparse observational data. The amplitude decay rate for crustal earthquakes in B.C. is very similar to that given by the empirical model of Bayless and Abrahamson (2018; hereafter, BA18), developed from California data on soil sites. However, we observe magnitude- and frequency-dependent differences between the models for ground-motion amplitude levels. We attribute these to (1) the different reference-site conditions of the models, with the B.C. GMMs being referenced to hard rock, and (2) steeper magnitude scaling at small-to-moderate magnitudes for events in B.C. in comparison to the BA18 model.

Performance evaluation of parameters as estimators of seismic site effects in northern South America

In this study, we investigate the performance of several parameters as estimators of seismic site effects for sites in northern South America. Investigated parameters include the conventional time-averaged shear wave velocity in the upper 30 m (VS30), the predominant period of the site, and horizontal-to-vertical spectral ratios. To assess the performance of these parameters, we estimate the amplification of seismic waves within shallow soil layers (i.e., site effects) at recording stations across northern South America. The site amplification is estimated by analyzing the residuals calculated from ground-motion records with respect to model predictions for hard-rock site conditions. Several functional forms were introduced to express the linear site amplification in terms of the explored parameters. We evaluate the efficacy of the parameters, as well as their advantages and limitations, by considering their impact in the site-to-site standard deviation of the residuals between observations and predictions using the introduced functional forms.

Data-driven adjustments for combined use of NGA-East hard-rock ground motion and site amplification models

Model development in the Next Generation Attenuation-East (NGA-East) project included two components developed concurrently and independently: (1) earthquake ground-motion models (GMMs) that predict the median and aleatory variability of various intensity measures conditioned on magnitude and distance, derived for a reference hard-rock site condition with an average shear-wave velocity in the upper 30 m ( VS30) = 3000 m/s; and (2) a site amplification model that modifies intensity measures for softer site conditions. We investigate whether these models, when used in tandem, are compatible with ground-motion recordings in central and eastern North America (CENA) using an expanded version of the NGA-East database that includes new events from November 2011 (end date of NGA-East data curation) to April 2022. Following this expansion, the data set has 187 events, 2096 sites, and 16,272 three-component recordings, although the magnitude range remains limited (∼4 to 5.8). We compute residuals using 17 NGA-East GMMs and three data selection criteria that reflect within-CENA regional variations in ground-motion attributes. Mixed-effects regression of the residuals reveals a persistent pattern in which ground motions are overpredicted at short periods (0.01–0.6 s, including peak ground acceleration (PGA)) and underpredicted at longer periods. These misfits are regionally variable, with the Texas–Oklahoma–Kansas region having larger absolute misfits than other parts of CENA. Two factors potentially influencing these misfits are (1) differences in the site amplification models used to adjust the data to the reference condition during NGA-East GMM development relative to CENA amplification models applied since the 2018 National Seismic Hazard Model (NSHM), and (2) potential bias in simulation-based factors used to adjust ground motions from the hard-rock reference condition to a VS30 = 760 m/s condition. We provide adjustment factors and their epistemic uncertainties and discuss implications for applications.

Comparison of surface-wave techniques to estimate S- and P-wave velocity models from active seismic data

Abstract. The acquisition of seismic exploration data in remote locations presents several logistical and economic criticalities. The irregular distribution of sources and/or receivers facilitates seismic acquisition operations in these areas. A convenient approach is to deploy nodal receivers on a regular grid and to use sources only in accessible locations, creating an irregular source–receiver layout. It is essential to evaluate, adapt, and verify processing workflows, specifically for near-surface velocity model estimation using surface-wave analysis, when working with these types of datasets. In this study, we applied three surface-wave techniques (i.e., wavelength–depth (W/D) method, laterally constrained inversion (LCI), and surface-wave tomography (SWT)) to a large-scale 3D dataset obtained from a hard-rock site using the irregular source–receiver acquisition method. The methods were fine-tuned for the data obtained from hard-rock sites, which typically exhibit a low signal-to-noise ratio. The wavelength–depth method is a data transformation method that is based on a relationship between skin depth and surface-wave wavelength and provides both S- and P-wave velocity (Vs and Vp) models. We used Poisson's ratios estimated through the wavelength–depth method to constrain the laterally constrained inversion and surface-wave tomography and to retrieve both Vs and Vp also from these methods. The pseudo-3D Vs and Vp models were obtained down to 140 m depth over an area of approximately 900 × 1500 m2. The estimated models from the methods matched the geological information available for the site. A difference of less than 6 % was observed between the estimated Vs models from the three methods, whereas this value was 7.1 % for the retrieved Vp models. The methods were critically compared in terms of resolution and efficiency, which provides valuable insights into the potential of surface-wave analysis for estimating near-surface models at hard-rock sites.

Ground-Motion Model for Hard-Rock Sites by Correction of Surface Recordings (Part 1): Comparison of Site-Response Estimates at KiK-Net Sites

ABSTRACT Site-specific seismic hazard assessment involves the prior knowledge of (1) the input ground motion at the local bedrock and (2) the site response. In this article and its companion, we address the deconvolution approach to obtain a reference ground-motion model, which consists of removing site effects from surface ground-motion recordings. Laurendeau et al. (2018) applied this approach on the KiK-net network with site response from 1D SH-wave (1DSH) simulations, calculated using the VS profiles available for most sites. Indeed, this approach presents several limitations with 1DSH site response if it is considered to be applied to other networks, especially in the European context. First, the approach requires identification of sites with dominant 1D effects. Second, it needs the presence of accurately measured VS profiles. In this context, we propose to derive deconvolved ground-motion models using site response from generalized inversion techniques () for two main reasons. The first reason is that the GIT delivers empirical site response for all types of sites, conditioned by the presence of sufficient amount of data, and the second is that it reduces the need for VS profiles. We focus on the estimation of site effects from different approaches and present a methodology to obtain reliable site terms from GIT based on the experience from previous studies. We also introduce and detail the difference between absolute and relative site response, which mainly depends on the chosen reference. We estimate and compare site response for the KiK-net stations with different methods, that is, empirical and theoretical 1DSH. We also conclude a list of 1D sites based on comparisons between theoretical and empirical estimates of site response. The results obtained in this article will be the primary input for the deconvolution approach applied in the companion article.

Ground-Motion Model for Hard-Rock Sites by Correction of Surface Recordings (Part 2): Correction, Mixed-Effects Regressions, and Results

ABSTRACT In the framework of site-specific seismic hazard assessment, the definition of reference motion is a crucial step. Reference motion is generally associated with hard-rock conditions, characterized by S-wave velocity exceeding 1500 m/s. However, ground motion recorded at sites with such conditions is poorly represented in existing strong-motion databases. Thus, the validity domains of most empirical ground-motion prediction equations (GMPEs) are not representative of reference rock conditions. To overcome this limitation and assess ground motion at reference conditions, the so-called “deconvolution approach” was proposed by Laurendeau et al. (2018) to correct surface recordings from theoretical 1DSH site response before GMPE developments. With the same purpose, in this article, we propose to apply the deconvolution approach using empirical site-response estimates as an alternative to theoretical ones. Using the Kiban–Kyoshin network (KiK-net) data, we estimate empirical site responses at KiK-net stations using generalized inversion techniques in addition to those from 1DSH numerical simulations, as presented in the companion article. Finally, a reference ground-motion model (RGMM) is determined based on empirically deconvolved ground motions. The advantage of using empirical rather than 1DSH site responses in the deconvolution approach is that in the former case the RGMM can be built based on records from an extensive set of sites, whereas the latter case is restricted to well-characterized sites with dominant 1D behavior. This makes the proposed approach easily exportable to different regions of the world, where precise site characterizations are not systematically available, and the knowledge of site behavior is limited.

Proposed Enhancements to the Risk-Informed and Performance-Based Regulatory Framework for Seismic Hazard Design at NRC-Regulated Nuclear Power Plants

The commercial nuclear power plant industry initiated the licensing modernization project (LMP) to enhance the risk-informed and performance-based (RIPB) regulatory basis for advanced nuclear power reactors. The LMP framework relies heavily on RIPB concepts and approaches that together integrate the defense-in-depth philosophy. One example approach for seismic design is to align the LMP concepts with the performance targets described in the American Society of Civil Engineers (ASCE) standard, ASCE 43-19. The underlying strategy of this approach is to consider the performance of individual structures, systems, and components (SSCs) in seismic design, as well as the role they play in an accident event sequence. This approach contrasts with current regulations, in which every individual safety-related SSC is designed to the same seismic criteria irrespective of the role the SSC plays in the overall system performance. This new philosophy envisions more flexible seismic design options for each SSC, such that the overall seismic design can meet system-level acceptability criteria as well as plant-level acceptability criteria. The objective of this paper is to illustrate the flexibility and benefits of this proposed approach to the seismic design of SSCs in terms of reduced SSC demands (by reducing the design ground motions for SSCs) and improved SSC capacities (by allowing for alternative damage state limits). A simple shear wall was designed using ASCE 43-19 for a hard rock site in the Central Eastern United States considering alternate seismic design category and limit state combinations to examine the physical designs and functional fragilities of these combinations and their impact on seismic performance. The flexibility of this proposed approach is illustrated by an example that shows reduced SSC demands, while the SSC capacities and margins remain consistent with the required safety performance without any loss in overall plant safety.

Frequency-dependent site amplification functions for key geological units in Iceland from a Bayesian hierarchical model for earthquake strong-motions

A fundamental modeling assumption in engineering seismology is that seismic ground motion is affected by source, propagation path and site effects. Contrary to the first two, comprehensive studies on site effects, the localized amplification effects on seismic ground motion due to the uppermost geological structure, have been limited in Iceland. As a result, site amplification has been modeled in ground motion models in a simplistic and qualitative way. In this study, we address this limitation by using the new Bayesian hybrid GMM proposed by Kowsari et al. (2020) to model the recorded ground motions at regional strong-motion stations in southwest Iceland, specifically the peak ground acceleration and pseudo-acceleration response spectra as a function of oscillator period (i.e., PGA and PSA at T=0.01-3.0 s), earthquake magnitude, distance and hypocentral depth, and at first, we omit a site-term. Then, we incorporate the GMM in a Bayesian Hierarchical Model (BHM) that allows prior distributions of model parameters to be used and we partition the model residuals into various terms associated with the source, propagation path and station terms. Through Bayesian inference of the model parameters the results show that the station term residuals reveal a frequency-dependent site amplification at the recording sites. By inspecting this systematic behaviour, we propose four groups of station terms by their characteristics. We then carefully inspect the station locations in terms of their associated geological unit and observe that the geological units and station term groups are qualitatively correlated. By combining the two, we propose the first frequency-dependent average site amplification functions associated with key geological units in Iceland based on age and formation. Provisionally we refer to them as hard rock, rock, (Holocene) lava rock, and (unspecified) soil site classes, respectively. We then update the GMM by incorporating these amplification functions so that it now enables the prediction of PGA and PSA at these four site classes. As a result, the new model standard deviations are considerably lower, with those associated with the event term being τ = 0.05, station terms φS2S = 0.10, intra-event φ = 0.17 and total σ = 0.18 in common logarithm units for PGA. The new site class-specific GMM now enables the site-specific ground motion for separate geological units which in turn improves site-specific seismic hazard assessment and informed site-specific engineering decision making in Iceland.

Research on seismic analysis methods of large and complex underground pipe structures in hard rock sites

In order to study the seismic design methods of large and complex underground pipe structures (LCUP) in hard rock sites, firstly, the structural characteristics of LCUP and the calculation principles of four typical seismic analysis methods were carefully sorted out. Secondly, based on different seismic analysis methods, the deformation and internal force response of three representative pipes were studied in detail, and the calculation accuracy and error causes of each seismic analysis method were analyzed. Finally, the advantages, disadvantages and applicability of the seismic analysis methods on typical pipes were systematically explained, and the technical route for seismic design of LCUP was proposed. The results showed that both the reaction displacement method and the reaction acceleration method can effectively analyze the seismic performance of standard section structures. The three-dimensional time-history analysis method was comprehensive and highly accurate for seismic analysis of complex spatial cross-node structures. The rigid connections of different pipes leaded to serious discontinuities in stiffness at the intersection, and the deformation and bending moment distributions were highly concentrated at the height away from the intersection. The influence range of the intersection was about three times the width of the intersection, and LCUP was classified according to this influence range. For standard section structures, seismic analysis should be carried out using the reaction acceleration method or reaction displacement method, while for spatial cross-node structures, three-dimensional time-history analysis should be used for seismic analysis. This scientific seismic design method achieved multiple optimal balances of seismic safety, analysis accuracy, efficiency and economy in the seismic analysis of large and complex underground structures. A theoretical basis and useful reference for the scientific design, accurate prediction and seismic safety evaluation of seismic response of LCUP were provided in this paper.

Deriving Site Effect-Free Hard-Rock Time Histories in Japan from the Generalized Inversion Technique

ABSTRACTA key component in seismic hazard assessment is the determination of time histories for hard-rock site conditions, either as input motion for site response computations or for applications to installations built on this site type. The state of the practice is to apply physics-based corrections for removing site effects from surface recordings to obtain the underlying bedrock motion. Here, we propose and test the use of the generalized inversion technique (GIT) for deconvolving surface recordings to hard-rock time series at the amplification-free seismic bedrock. As part of the proposed procedure, an event-specific phase scaling method is presented, which allows changes in signal duration to be considered. For validation purposes, we select a total of 90 Kiban–Kyoshin network (KiK-net) surface-downhole sites having no significant velocity contrasts below their downhole sensors and with the latter being located at sufficient depth so that they are not impaired significantly by downgoing waves. We evaluate the effectiveness of the empirical predictions by comparison with recorded time series at the downhole sensors. We find quite high correlations and small variations in both spectral shape and amplitude over the entire frequency range for the GIT deconvolution at the majority of the 90 KiK-net sites with all mean residuals less than 0.25 in contrast to empirical and 1D modeling approaches, which significantly overestimate the level of hard-rock ground motion for frequencies larger than a few Hertz.

Hard-rock investigation using a non-invasive geophysical approach

Investigation of a hard-rock terrain is essential for the development of engineering infrastructures and groundwater assessment. In such investigations, evaluation of rock mass quality and faults/fractures is a challenging task. Conventionally, borehole tests are conducted to acquire subsurface geological information, and rock mass quality parameters such as rock quality designation (RQD). However, such tests are expensive, slow, limited to some specific locations, require more equipment, provide point measurements, and are hardly conducted in a steep topographic terrain. Generally, the non-invasive geophysical methods, such as geoelectrical methods are performed to assess the hard-rock sites. However, such parameters alone provide ambiguity in interpreting the geological units. In this work, a joint approach of four geophysical parameters (e.g., electrical resistivity (ER), self-potential (SP), magnetic, and induced polarization (IP)) is proposed to assess a highly heterogeneous terrain for the installation of the Accelerator Driven System (ADS) facility in South China. Geophysical data were obtained via a variety of surveyed parameters along different profiles. Electrical resistivity tomography (ERT) was integrated with borehole tests data to determine RQD for rock mass quality evaluation over the entire area. The results of magnetic interpretation were calibrated with well data to constrain the subsurface into distinct layers. ERT and magnetic coupled with Joint Profile Method (JPM) detected several localized faults/fractures. IP was integrated with ERT to distinguish between water and clay. Groundwater flow path was marked using SP. Compared with the past investigations, this novel approach deciphers functional analogous relation of RQD with ERT, magnetic, IP and SP in the hard-rock, provides thorough insights into the subsurface, removes the ambiguity caused by single geophysical parameter or the inadequate well data, and bridges the gaps between accurate geological model and the limited data for the development of engineering structures and groundwater resources.

GMPE-consistent hard-rock site adjustment factors for Western North America

Empirical ground-motion prediction equations (GMPEs) such as the Next Generation Attenuation-West2 (NGA-West2) GMPEs are limited in the number of recordings on hard-rock stations used to develop the models. Therefore, the site response scaling in the GMPEs cannot be reliably extrapolated to hard-rock conditions. The state of practice for the development of hard-rock adjustment factors involves the use of analytical methods that typically assign small values to the small-strain damping parameter ([Formula: see text]) for hard-rock sites resulting in large scaling factors at short periods. Alternatively, the hard-rock scaling factors developed in Ktenidou and Abrahamson (KA16) based on empirical ground-motion data are used. These empirical factors, developed for a broad rock site category, show that the average hard-rock scaling factors observed in ground-motion data are small in amplitude contrary to the large factors typically obtained from analytical studies. The empirically derived KA16 factors also suffer from limitations due to the relatively small number of rock sites in the data set and do not distinguish between different hard-rock conditions. To address the shortcomings in the current state of practice, we present a methodology to develop linear site adjustment factors to adjust the NGA-West2 GMPEs from V S30 of 760 m/s to target hard-rock site conditions with V S30 ranging from 1000 to 2200 m/s. These factors are analytically derived using the inverse random vibration theory (IRVT) approach of Al Atik et al. but with inputs constrained using the empirical KA16 factors and normalized to the scaling of the NGA-West2 GMPEs for V S30 of 1000 m/s. The proposed factors merge the results of the NGA-West2 site response scaling for V S30 ≤ 1000 m/s with the KA16 hard-rock category factors to produce a site factor model that is a continuous function of V S30. The epistemic uncertainty of these factors is evaluated.

Surface-wave tomography for mineral exploration: a successful combination of passive and active data (Siilinjärvi phosphorus mine, Finland)

Abstract. Surface wave (SW) methods offer promising options for an effective and sustainable development of seismic exploration, but they still remain under-exploited in hard rock sites. We present a successful application of active and passive surface wave tomography for the characterization of the southern continuation of the Siilinjärvi phosphate deposit (Finland). A semi-automatic workflow for the extraction of the path-average dispersion curves (DCs) from ambient seismic noise data is proposed, including identification of time windows with strong coherent SW signal, azimuth analysis and two-station method for DC picking. DCs retrieved from passive data are compared with active SW tomography results recently obtained at the site. Passive data are found to carry information at longer wavelengths, thus extending the investigation depth. Active and passive DCs are consequently inverted together to retrieve a deep pseudo-3D shear-wave velocity model for the site, with improved resolution. The southern continuation of the mineralization, its contacts with the host rocks and different sets of cross-cutting diabase dikes are well imaged in the final velocity model. The seismic results are compared with the latest available geological models to both validate the proposed workflow and improve the interpretation of the geometry and extent of the mineralization. Important large-scale geological boundaries and structural discontinuities are recognized from the results, demonstrating the effectiveness and advantages of the methods for mineral exploration perspectives.

Analysis of Crustal Stress and Its Influence on the Stability of the Deep Tunnel in the Huanaote Mining Area

Crustal stress is a critical parameter utilized to analyze the stability of the tunnel in underground hard‐rock mining sites. In order to analyze the distribution law of crustal stress and its influence on the stability of the deep tunnel in the Huanaote mining area, the in‐situ stress field model of this area was constructed firstly by using the borehole stress relief method. Moreover, the numerical model is established based on three real engineering conditions: the excavation direction is parallel, vertical, and intersection to the measured maximum horizontal principal stress direction, respectively. Results show that, compared with the other two layout schemes, the stress of two side walls reaches peak at 27 MPa, when the excavation direction is intersected to the measured maximum horizontal principal stress direction, which indicates that the support and maintenance of two side walls should be strengthened to ensure the stability of the tunnel and the safety of personnel and equipment in real projects.

Broadband ground motion simulations for Northeast India

This study presents broadband (BB) ground motions for two historical earthquakes (Mw ≥ 8) in Northeast (NE) India. We apply a recently developed geology-based 3D velocity model of the Northeastern region (NER) to simulate low frequency (LF) ground motions (f < 1Hz). These synthetics are further combined with high frequency (HF) scattering wave-fields (f > 1Hz) using a hybrid approach, thus yielding BB ground motions (0.1–10Hz). First, we calibrate the 3D model and scattering parameters by comparing the simulated ground motions against recorded data available for four events (Mw 5.2, Mw 5.5, Mw 6.3, and Mw 7.2) in NE India. Our results indicate that the variability of the bias for spectral acceleration (SA) lies within limits [-1,1] for all four events. From the statistical analysis of the ground motion, we also observe that the hybrid approach gives a realistic estimation of site-specific BB ground motion and consistently reproduces the prominent features of the observed motions up to 10Hz at most of the stations. Next, we simulate a suite of BB ground motions to estimate ground motion intensities for two historical earthquakes (viz., 1897 Assam event, 1950 Assam event) in NE India. Our results indicate that the variations in the ground motion intensities at hard rock and soft soil sites are manifestations of the local geology and surface topography incorporated in the 3D regional velocity model. We also observe that the peak ground acceleration (PGA) for both events exceed 1 g in the epicentral region. The BB ground motions obtained from this approach will be useful to engineers in seismic design and site-specific hazard estimation.

Integration of ERT, IP and SP Methods in Hard Rock Engineering

Investigation of a hard rock site for the development of engineered structures mainly depends on the delineation of weathered and unweathered rock, and the fractures/faults. Traditionally, borehole tests are used in such investigations. However, such approaches are expensive and time-consuming, require more equipment, cannot be conducted in steep topographic areas, and provide low coverage of the area with point measurements only. Conversely, geophysical methods are non-invasive, economical, and provide large coverage of an area through both vertical and lateral imaging of the subsurface. The geophysical method, electrical resistivity tomography (ERT), can reduce a significant number of expensive drilling tests in geotechnical investigations. However, a geophysical method alone may provide ambiguity in the interpretation of the subsurface, such as electrical resistivity cannot differentiate between water and clay content. Such uncertainty can be improved by the integration of ERT with induced polarization (IP). Similarly, self-potential (SP) can be integrated with other geophysical methods to delineate the groundwater flow. In this contribution, we integrated three geophysical methods (ERT, IP and SP) to delineate the weathered and unweathered rock including the weathered/unweathered transition zone, to detect the fractures/faults, and to map the groundwater flow. Based on ERT, IP and SP results, we develop a geophysical conceptual site model which can be used by site engineers to interpret/implement the findings for build-out. Our approach fills the gaps between the well data and geological model and suggests the most suitable places for the development of engineered structures in the hard rock terrains.

Joint geophysical prospecting for groundwater exploration in weathered terrains of South Guangdong, China.

Groundwater occurrence in a hard rock terrain is strongly controlled by the weathered/fractured zones. However, delineation of such zones is a challenging task given their structural heterogeneity. Traditionally, large numbers of well tests are conducted to assess the subsurface formation. But, such tests suffer from efficiency in terms of cost, time, and data coverage. Non-invasive geophysical methods can be the best alternative of expensive drilling methods. However, a geophysical method alone is ambiguous to interpret the highly heterogeneous subsurface formation. In this study, joint application of electrical resistivity tomography (ERT), magnetic method, and joint profile method (JPM) was conducted for groundwater exploitation in a weathered terrain of South Guangdong, China. ERT, magnetic, and JPM data were acquired along different geophysical profiles via a variety of survey parameters. The interpreted 2D models of electrical resistivity and magnetic data coupled with the local accessible boreholes and hydrogeological information constrain the subsurface geologic formation into four discrete layers with specific electrical resistivity range, i.e., topsoil cover, highly weathered saturated layer, semi-weathered saturated layer, and un-weathered substratum. Incorporation of JPM (ER, SP, and IP methods) with ERT and magnetic models reveal three faults (F1, F2, and F3) and several saturated intense fractures/discontinuities. The groundwater reserves associated with the weathered/fractured rock were estimated via hydraulic parameters, namely hydraulic conductivity and transmissivity. The results suggest that high-yield groundwater resources are found within the weathered/fractured zones. Geophysical results of this joint application fit pretty well to the local hydrogeological data of the study area. Our novel approach reduces any ambiguity caused in the geophysical interpretation and provides clearer insight of the subsurface formation with more confident solutions to the most challenging problems of the hard rock sites. This hydrogeophysical study provides important contributions to groundwater exploration in areas where weathering has significant effects on the hard rock aquifer system. Compared with traditional methods, this approach is more advantageous for assessment of groundwater resources in hard rock terrains.

Variation Evaluation of Path Characteristic and Site Amplification Factor of Earthquake Ground Motion at Four Sites in Central Japan

The considered parameters in seismic design vary, with the Earthquake Ground Motion (EGM) having the largest variation. Since source characteristic, path characteristic, and Site Amplification Factor (SAF) influence the EGM, it is crucial to appropriately consider their variations. Source characteristic variations are mainly considered in a seismic hazard analysis, which is commonly used to evaluate variations in EGM. However, it is also important to evaluate variations in path characteristic and SAF with only a few studies having individually and quantitatively examined the variations of these two characteristics. In this study, based on strong-motion observation records obtained from four sites in central Japan, the three characteristics were extracted from seismograms using the concept of spectral inversion. After removing the source characteristic, the path characteristic and SAF were separated, and the variations in these two characteristics were quantified. To separate and obtain each characteristic from the observed record, one constraint condition must be imposed, whereas the variations in the constraint condition must be ignored. In that case, the variations in the constraint condition are included in the variations of the separated characteristics. In this study, this problem was solved by evaluating the variation in the constraint condition, which is the SAF at a hard rock site, by the use of the vertical array observation record at the site.