Site Response Studies Research Articles

Deep Shear Wave Velocity Profiles from Surface Wave Measurements in the Mississippi Embayment

Shear wave velocity ( VS) profiles to depths of approximately 200 m were developed from active-source surface wave velocity measurements in the Mississippi Embayment region of the Central United States. Soil deposits in this region are hundreds of meters thick, but are poorly characterized at depths below 60 m. Measurements were performed at five locations in Arkansas and Tennessee with a maximum distance between sites of approximately 130 km. The median VS profile calculated from the five profiles is in good agreement with a generic reference VS profile for the Mississippi Embayment that has been used in recent site response studies. The near-surface VS profiles at the five sites were remarkably consistent with average shear wave velocities in the top 30 m ( VS30), varying by less than 10%. Increasing variability between the VS profiles was observed at greater depths. The variability between VS profiles was shown to be correlated with changes in lithology at two of the sites where nearby lithologic information was available.

First Order Seismic Microzonation of Delhi, India Using Geographic Information System (GIS)

A first order seismic microzonation map of Delhi is prepared using five thematic layers viz., Peak Ground Acceleration (PGA) contour, different soil types at 6 m depth, geology, groundwater fluctuation and bedrock depth, integrated on GIS platform. The integration is performed following a pair-wise comparison of Analytical Hierarchy Process (AHP), wherein each thematic map is assigned weight in the 5-1 scale: depending on its contribution towards the seismic hazard. Following the AHP, the weightage assigned to each theme are: PGA (0.333), soil (0.266), geology (0.20), groundwater (0.133) and bedrock depth (0.066). The thematic vector layers are overlaid and integrated using GIS. On the microzonation theme, the Delhi region has been classified into four broad zones of vulnerability to the seismic hazard. They are very high (> 52%), high (38–52%), moderate (23–38%) and less ( < 23%) zones of seismic hazard. The “very high” seismic hazard zone is observed where the maximum PGA varies from 140 to 210 gal for a finite source model of Mw 8.5 in the central seismic gap. A site amplification study from local and regional earthquakes for Delhi region using Delhi Telemetry Network data shows a steeper site response gradient in the eastern side of the Yamuna fluvial deposits at 1.5 Hz. The ‘high’ seismic hazard zone occupies most of the study area where the PGA value ranges from 90 to 140 gal. The ‘moderate’ seismic hazard zone occurs on either side of the Delhi ridge with PGA value varying from 60 to 90 gal. The ‘less’ seismic hazard zone occurs in small patches distributed along the study area with the PGA value less than 60 gal. Site response studies, PGA distribution and destruction pattern of the Chamoli earthquake greatly corroborate the seismic hazard zones estimated through microzonation on GIS platform and also establishes the methodology incorporated in this study.

Variations in Short-period Geophone Responses in Temporary Seismic Arrays

Geophones with resonant frequencies of 1–4 Hz are commonly used as short-period sensors for site-response studies ( e.g. , Bonilla et al. , 1997; Hartzell et al. , 1997; Frankel et al. , 1999; Hartzell et al. , 2000) and crustal-reflection, refraction, and tomography experiments ( e.g. , Brocher et al. , 2001; Fuis et al. , 2003). In many cases these studies require only arrival-time picks, but site-response and attenuation measurements require accurate ground-velocity data from these sensors. Moreover, these geophones are often used to record seismic phases at or below their nominal resonant frequencies ( e.g. , Bonilla et al. , 1997; Hartzell et al. , 2000; Dutta et al. , 2001; Pratt et al. , 2003b; Pratt et al. , 2003a). For studies that require accurate ground-velocity measurements or that use a variety of sensor types, the instrument response must be removed from the data using either the manufacturer's specifications or results from geophone calibration tests. Geophone placement, particularly any tilt to the sensor, can alter the instrument response significantly. The geophone response ideally is measured while the sensors are in the ground, but such in situ calibrations generally are not carried out because of time constraints. More commonly, it simply is assumed the geophones have the response characteristics specified by the manufacturer. In a recent site-response study in the Seattle area, named the Seattle Seismic Hazard Investigation of Puget Sound (Seattle SHIPS 2002; Pratt et al. , 2003b), we used 72 three-component geophones from the Program for Array Seismic Studies of the Continental Lithosphere (PASSCAL) instrument pool to determine the amplitudes of both horizontal and vertical ground shaking at sites over the Seattle sedimentary basin (Pratt et al. , 2003b). During the experiment, we used the signal-coil calibration method (Rogers …

A Comparison of Site Response Techniques Using Weak-Motion Earthquakes and Microtremors

The applicability of the microtremor spectral ratio method is examined by comparing microtremor and weak-motion earthquake site responses at seven permanent strong-motion sites in Victoria, British Columbia. For each site, a weak-motion earthquake standard spectral ratio (bedrock reference), the average horizontal-to-vertical spectral ratio of up to five weak-motion earthquakes, and the average microtremor (Nakamura method) spectral ratio are compared. The geologic setting of Victoria is ideal for site response studies with a near-surface high impedance contrast between thin geologic layers of Victoria clay (about 11 m maximum in this study) and Pleistocene till or bedrock. Regardless of excitation source (weak-motion earthquakes or microtremors) and spectral ratio method, similar peak amplitudes and fundamental frequencies were found. Thicker material (&gt;10 m) sites displayed higher peak amplitudes (up to six times amplification) at frequencies of 2–5 Hz compared to sites with a thin lens of material (&lt;3 m) over bedrock that showed peak amplitudes at frequencies of &gt;8 Hz.

On the correlation of seismic microtremors

We present results of the analysis of microtremor measurements using a small array. Our analysis is based on the computation of cross‐correlation functions between stations in both frequency and time domains. We obtain similar results in both domains and link those results to the application of Aki's spatial autocorrelation method of using a single station pair and to recent studies that have shown that the Green's function between two stations can be retrieved from the temporal cross correlation of seismic noise. We show that the same simple subsoil structure allows interpretation of our correlation results in time and frequency. We observe both Love and Rayleigh waves; however, Love waves dominate the records in our lower‐frequency range (between 3.6 and 6 Hz), while Rayleigh waves are prevalent in the records in our higher‐frequency band (from 6 to 20 Hz). Frequency domain cross correlation yields better results in the lower‐frequency range, while time domain cross correlation shows very clear results in the higher‐frequency band. Thus both analyses are complementary. Our results show that ambient vibration recorded at the free surface includes different types of waves but that the correlation between any two stations is governed by the more stable propagation mode between them, surface waves in the case of a layered medium. Our results shed some light on the nature of microtremors and on the reasons why the spatial autocorrelation method or the horizontal‐to‐vertical spectral ratios are useful in geophysical and site response studies.

Site Effect Evaluation In Sellano (Italy) By1-D And 2-D Numerical Analyses

The 1997–1998 Umbria-Marche seismic sequence induced severe damage to the historical centre of Sellano (Perugia, Italy). During the long aftershock sequence two temporary accelerometric stations, about 300m apart, provided several ground motion records. These data allowed us to investigate the amplification of surface motion which can essentially be ascribed to local seismic effects. A site response study of the historical centre of the village was carried out by means of 1-D and 2-D numerical analyses to clarify the role played by the stratigraphic and topographic effects. The applicability of 1-D and 2-D models was examined by comparing the recorded and calculated acceleration response spectra. 1-D response analyses seem to indicate a significant stratigraphic effect on the ground response. Conversely, 2-D response analyses have shown only moderate amplification effects due to surface topography, which somewhat improved the predictions of site response spectra.

The influence of wind on measurements of seismic noise

SUMMARY The horizontal to vertical spectral ratio (HVSR) technique of microtremor measurement is widely applied in microzonation and site response studies. Given the small amplitude of the measured signal, unwanted disturbances may adversely affect the results. We analysed the influence of local wind on microtremor measurements as follows: first, we studied variation in HVSR at a permanent, three-component seismological station under various wind patterns; second, we conducted an experiment under controlled condition in a wind room equipped with a laser particle image velocimeter, analysing the effect of increasing wind speed on various sensor/digitizer configurations; third, we undertook numerical modelling to explain the observed data. Our main conclusions are that wind increases the amplitude of all components of the microtremor wavefield, but does not affect HVSR; however, certain sensor/digitizer configurations can be adversely affected by instrumental noise due to turbulence at the air/instrument/ground interface.

Nonlinear shear mass participation factor ( rd) for cyclic shear stress ratio evaluation

Most methods for assessment of in situ seismic soil liquefaction potential require evaluation of the earthquake-induced cyclic shear stress ratio (CSR). Estimates of the in situ CSR can be developed directly, using dynamic response analyses, but it is common in ‘simplified’ analysis methods to develop estimates of the in situ CSR using empirical relationships. Unfortunately, the most widely used existing empirical relationships are based on limited response analyses and do not take full advantage of current knowledge of factors affecting this response problem. As a result, they are both biased and unnecessarily imprecise. This paper presents the results of a relatively comprehensive suite of site response studies (2153 site response analyses), performed using carefully selected suites of site conditions and input time histories, to provide an improved basis for development of estimates of in situ CSR using the r d -approach. The resulting empirical correlations, developed using the Bayesian updating method, provide a much improved basis for simplified empirical evaluation of CSR as a function of (1) depth; (2) earthquake magnitude; (3) intensity of shaking; and (4) site stiffness.

Urban seismic experiments investigate Seattle Fault and Basin

In the past decade, Earth scientists have recognized the seismic hazards that crustal faults and sedimentary basins pose to Seattle, Washington (Figure 1). In 1998, the US. Geological Survey and its collaborators initiated a series of urban seismic studies of the upper crust to better map seismogenic structures and sedimentary basins in the Puget Lowland. These studies are called the Seismic Hazard Investigations of Puget Sound (SHIPS).In March 1998, we conducted our first SHIPS study, an investigation of the upper crustal structure of the Puget Lowland, using marine airgun sources and land recorders [Fisher et al., 1999].The study was nicknamed Wet SHIPS. In September 1999, we obtained a seismic refraction line to study the upper crustal structure in the Seattle area in a land‐based study nicknamed Dry SHIPS [Brocher et al., 2000] (Figure 1). In March 2000, we recorded the demolition of the Seattle Kingdome sports stadium using a dense array of seismic recorders for a detailed site response study; this study was nicknamed Kingdome SHIPS (Figure 1).

CityShark: A User-friendly Instrument Dedicated to Ambient Noise (Microtremor) Recording for Site and Building Response Studies

Research Article| November 01, 2000 CityShark: A User-friendly Instrument Dedicated to Ambient Noise (Microtremor) Recording for Site and Building Response Studies Jean-Luc Chatelain; Jean-Luc Chatelain 1IRD, Quito, Ecuador 2LGIT, Grenoble, France Search for other works by this author on: GSW Google Scholar Philippe Gueguen; Philippe Gueguen 1IRD, Quito, Ecuador 2LGIT, Grenoble, France Search for other works by this author on: GSW Google Scholar Bertrand Guillier; Bertrand Guillier 1IRD, Quito, Ecuador 3EPN, Quito, Ecuador Search for other works by this author on: GSW Google Scholar Julien Frechet; Julien Frechet 2LGIT, Grenoble, France Search for other works by this author on: GSW Google Scholar Francis Bondoux; Francis Bondoux 1IRD, Quito, Ecuador 3EPN, Quito, Ecuador Search for other works by this author on: GSW Google Scholar Jacques Sarrault; Jacques Sarrault 4LEAS, St Ismier, France Search for other works by this author on: GSW Google Scholar Pascal Sulpice; Pascal Sulpice 4LEAS, St Ismier, France Search for other works by this author on: GSW Google Scholar Jean-Marc Neuville Jean-Marc Neuville 4LEAS, St Ismier, France Search for other works by this author on: GSW Google Scholar Seismological Research Letters (2000) 71 (6): 698–703. https://doi.org/10.1785/gssrl.71.6.698 Article history first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Jean-Luc Chatelain, Philippe Gueguen, Bertrand Guillier, Julien Frechet, Francis Bondoux, Jacques Sarrault, Pascal Sulpice, Jean-Marc Neuville; CityShark: A User-friendly Instrument Dedicated to Ambient Noise (Microtremor) Recording for Site and Building Response Studies. Seismological Research Letters 2000;; 71 (6): 698–703. doi: https://doi.org/10.1785/gssrl.71.6.698 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySeismological Research Letters Search Advanced Search CityShark, a station dedicated to ambient noise (microtremor) recording, was designed and built jointly by the French Institute for Research for Development (IRD) and LEAS, a French company dedicated to geophysical data acquisition. Because portable seismic stations are designed to be installed for long time periods (days to months) and to detect earthquakes, operators using them for microtremor recording face several obstacles that considerably slow and complicate the data acquisition process. Seismological stations are not easy to use in experiments for which time of recording is on the order of tens of minutes (site studies) or for repetitive recording of... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Site response studies for low seismicity regions of Central Europe: research strategies in support of code development

According to ENV 1998-1-1 (Eurocode 8) the influence of local ground conditions on the seismic action is accounted for by considering three subsoil classes (A,B,C) being described by different stratiggraphic profiles. These profiles are mainly distinguished by shear wave velociteies v s (in a certain depth) and by a global description of subsoil properties. Fromauthor's studies it can be concluded that the proposed classifications of ground conditions will not cover predominant site conditions of Central Europe and, furthermore, that it is not free of inconsistencies regarding practical application. Therefore, site investigations studies were initiated to consider the peculiarities of spectral amplification in dependence of soil profile, thickness of individual layers as well as the stiffness contrast betwen them, and variations of v s-values in more detail. Using analytical wave propagation method in one-dimensional horizontally layered soil deposits numerous parameter studies have been carried for defining site-dependent spectra in code-like parameters (EC 8). From these results it could be concluded that—under the pre-assumption of a fixed amplification factor β 0 ( β 0=2.5)—it is not possible to define sites effects in a realistic manner. Therefore it will be recommended to split the single soil factors S into factors S 1 (at T≥0) and S2 (for T≥ T B), or even more factors.

Site response study in Abruzzo (Central Italy): underground array versus surface stations

In this site response study we examined local earthquakes recorded at surface stations of a local seismic network and at a temporary underground seismic array installed in a tunnel underneath the Gran Sasso Massif in Abruzzo (central Italy). This allowed us to compare the seismic site response beneath the mountain and on the surface in similar geological environment (soft rock sites). We applied spectral ratios method on different segments of the seismograms and used different reference spectra in the 1–20 Hz frequency band. We found little or no amplification effects at most of the surface stations whereas site transfer functions evaluated with respect to underground sites show an amplification factor up to 6 in the 1–8 Hz frequency range. Coda spectral ratios estimated at soft rock sites are confirmed as good estimates of shear wave transfer function.

Estimated Magnitudes and Accelerations Associated with Prehistoric Earthquakes in the Wabash Valley Region of the Central United States

Seismic hazards in the central United States are typically based on occurrences of earthquakes in the New Madrid Seismic Zone. However, paleoliquefaction evidence shows that large prehistoric earthquakes also occurred in the Wabash Valley region of Indiana and Illinois. A geotechnical study of the soil conditions at paleoliquefaction sites there is used to estimate both the magnitudes and accelerations of the prehistoric earthquakes. This study covers an area of the Wabash River drainage approximately 250 km north to south and 180 km east to west, in southern Indiana and Illinois. In situ soil strength parameters were measured at 22 sites. The measured strength parameters are used in conjunction with liquefaction susceptibility analyses to estimate moment magnitude ( M ) and peak surface accelerations of four separate paleoearthquakes. In addition, site response studies based on the Atkinson and Boore (1995) model of bedrock motions for eastern North American earthquakes are used to develop attenuation relations. This allows a comparison of the results of the geotechnical study with a seismological prediction of peak surface accelerations due to the paleoearthquakes. Using a regionally appropriate relationship between magnitude and maximum distance to liquefaction effects (Obermeier et al. , 1993) leads to preliminary magnitude estimates of M 6.8, M 6.9, M 7.2, and M 7.8 for the four paleoearthquakes. Also, a method we developed, an energy-stress approach, is used to estimate the peak surface accelerations at these magnitudes that would be required to induce the observed liquefaction effects. Next, the acceleration estimates are compared with peak surface motions predicted by a seismological attenuation model for various magnitudes in order to determine the best-fitting magnitude. For the four paleoearthquakes studied, the geotechnical and seismological estimates of surface accelerations most closely agree for M 6.9, M 7.1, M 7.3, and M 7.8. Thus, two different methods yield basically the same paleomagnitudes, and therefore provide our best estimates.

Site Response Studies for Purpose of Revising NEHRP Seismic Provisions

A strong motion database was compiled for California earthquakes of surfacewave magnitudes, Ms ≥ 6, occurring from 1933 through 1992. The database consisted of horizontal peak ground acceleration and 5 percent damped response spectra of accelerograms recorded on four different local geologies: rock (class A), soft rock or stiff soil (class B), medium stiff soil (class C), and soft soil (class D). The results of analyses of the database within each of these site classes were used to derive a set of site-dependent spectral amplification factors for oscillator periods between 0.1 and 4.0 sec and ground acceleration levels between 0.1 and 0.4 g. The amplification factors at 0.3 and 1.0 sec periods (designated as Fa and Fv, respectively) are generally within 20 percent of those recommended during the 1992 Site Response Workshop conducted by the National Center for Earthquake Engineering Research (NCEER). The Fa and Fv values recommended from our study and those from the NCEER workshop are intended for use by code committees making future revisions to the National Earthquake Hazard Reduction Program (NEHRP) seismic provisions and the Uniform Building Code.

Earthquake site-response study in Giumri (formerly Leninakan), Armenia, using ambient noise observations: E. H. Field & 9 others, Bulletin — Seismological Society of America, 85(1), 1995, pp 349–353

Earthquake site-response study in Giumri (formerly Leninakan), Armenia, using ambient noise observations: E. H. Field & 9 others, Bulletin — Seismological Society of America, 85(1), 1995, pp 349–353

Earthquake site-response study in Giumri (formerly Leninakan), Armenia, using ambient noise observations

We have tested whether ambient noise observations reveal useful information regarding site response at sediment sites in Giumri (formerly Leninakan), Armenia. This was done by comparing the noise observations with spectral-ratio site-response estimates based on aftershock data of the 7 December 1988 earthquake. We show that neither the horizontal-component noise spectra alone, nor spectral ratios taken with respect to a nearby bedrock site, reveal useful information regarding site response. However, spectral ratios of horizontal components taken with respect to vertical components (Nakamura's method) exhibit a prominent peak that corresponds to the fundamental resonant frequency observed in the aftershock data. Based on this and other recent investigations, we conclude that Nakamura's method may be a reliable procedure for determining the fundamental resonant frequency of sedimentary deposits from ambient noise observations.

Monte-Carlo Simulation of the Theoretical Site Response Variability at Turkey Flat, California, Given the Uncertainty in the Geotechnically Derived Input Parameters

In the weak-motion phase of the Turkey Flat blind-prediction effort, it was found that given a particular physical model of each sediment site, various theoretical techniques give similar estimates of the site response. However, it remained to be determined how uncertainties in the physical model parameters influence the theoretical predictions. We have studied this question by propagating the physical parameter uncertainties into the theoretical site-response predictions using monte-carlo simulations. The input-parameter uncertainties were estimated directly from the results of several independent geotechnical studies performed at Turkey Flat. While the computed results generally agree with empirical site-response estimates (average spectral ratios of earthquake recordings), we found that the uncertainties lead to a high degree of variability in the theoretical predictions. Most of this variability comes from poor constraints on the shear-wave velocity and thickness of a thin (∼2m) surface layer, and on the attenuation of the sediments. Our results suggest that in site-response studies which rely exclusively on geotechnically based theoretical predictions, it will be important that the variability resulting from input-parameter uncertainties is recognized and accounted for.

Variation of Site Response at the UCSB Dense Array of Portable Accelerometers

Ten Kinemetrics model SSA-2 Solid State Accelerographs were deployed in two dense arrays following the Landers-Big Bear earthquake sequence. The two arrays were separated by approximately three km, the first at a shallow alluvial soil site and the second at a rock site. We examine the soil and rock sites in terms of spectral ratio and cross-spectrum estimates of the site response. In order to construct an accurate representation of the motion in the horizontal plane, we treat the two horizontal components simultaneously as a complex signal. The Fourier transform of this complex signal represents the true motion in the horizontal plane as expressed in the frequency domain. The spectral ratio estimate is the ratio of this Fourier transform at the soil sites to the rock sites. The cross-spectrum estimate is the ratio of the cross-spectral density between the soil and rock sites to the power spectral density of the rock site. Spectral ratio estimates of site amplification are consistently higher than cross-spectrum estimates. On average the soil sites show amplification factors on the order of 2 to 4 relative to the rock sites between the frequencies of 4 to 15 Hz. There are, however, large variations in the ground motion recorded at sites with separations as small as 80 m. These variations demonstrate that site response studies can be biased by the choice of location of the sensor at distances of 80 m. We conclude that in the analysis of site-specific amplification both cross-spectrum and spectral ratio techniques should be used along with ensemble averages over many events.

Site response effects for structures located on sand sites

Results are presented for 4 sand sites forming part of a site response study of 11 soil sites. The results are in the form of spectral accelerations and ratios, base shear coefficients, and foundation factors. They indicate that significant amplifications can be expected at sand sites, especially for low-intensity excitation. Comparisons are made with the provisions of the proposed National Building Code of Canada (NBCC) 1990. They show that, depending on the site and the nature and level of the excitation, the expected base shears can be well in excess of the values specified by the NBCC. Key words: seismic, design, sand, soil, site, response, spectra, amplification, base, shear.

Earthquake site response study of Accra area, Ghana

Earthquake site response study of Accra area, Ghana