Local Site Effects Research Articles

Adaptive pattern of phenotypic plasticity and inherent growth reveal the potential for assisted transfer in sessile oak (Quercus petraea L.)

Based on data published by Sáenz-Romero et al. (Adaptive and plastic responses of Quercus petraea populations to climate across Europe, 2017), an alternative reanalysis of a continent-wide common garden experiment (provenance test) of sessile oak was performed. Population mean heights were analyzed with a focus on responses to drought and high summer temperatures projected for the future. The main aim was to assess the adaptive capacity of populations in the critical drying and warming domain of the distribution. A unilateral approach was applied to calculate response regressions (reaction norms) of individual populations. Regression parameters served to investigate the changing balance of growth potential, phenotypic plasticity and resilience among populations of different provenance.Among the reanalysis results, the most striking was the flat, quasi-linear response in the dry-warm niche domain reaching beyond the mimicked “local” conditions. Consequently, at climates equivalent to the population origins no maxima were found. Populations from humid-cool climates displayed higher climate sensitivity (plasticity) to changes toward drier and warmer climates. Populations of dry-warm provenance have shown higher resilience under changing climate. Inherent height growth potential of populations in climates similar to that at their origin (“virtual height”) diminished significantly with increasing aridity at provenance. Growth potential and resilience revealed a selection trade-off among populations and both appeared as traits under climatic (adaptive) selection.Thus, assisted transfer of sessile oak populations may improve resilience; however, at the expense of lower growth potential. This cautions against mixing differently adapted populations in artificial regenerations. The use of local provenances as a recommended adaptive measure indicates limited relevance for sessile oak.The present generation of forest trees meets the predicted rapid climate/habitat shifts in its lifetime. Therefore, phenotypic plasticity and resilience will play a central role in sustaining the fitness of extant populations. To determine these traits independently from local site effects, common garden data cannot be neglected and are worth reanalyzing. Notably, provenance tests provide real-time field information on the performance of populations in new climatic environments, applicable for assisted transfer initiatives.

Local Site Effects in Definition of Seismic Design Parameters for Historical Monuments

Presented in this paper are investigations related to local site conditions carried out for seismic assessment of two historical structures in Macedonia: the Church of the Holy Mother of God Peribleptos dating back to the 13th Century and located in the old town of Ohrid, and the Mustafa Pasha Mosque in Skopje dating back to the 15th Century. The objective of the described procedure has been to take into consideration the regional and microlocation geological and seismological parameters in order to define the input seismic parameters for dynamic analysis of the historical structures. The obtained results have pointed out the significance of involving local site conditions in seismic assessment and retrofitting of historical structures in general. The procedure has been applied to many buildings of historical importance requiring strengthening and rehabilitation with great success and efficiency.

Estimation of earthquake local site effects using microtremor observations for the Garhwal–Kumaun Himalaya, India

ABSTRACTThe Garhwal–Kumaun region of the Himalaya encompassing the state of Uttarakhand, India, has experienced several earthquakes in the past. Damage due to earthquakes is controlled by local site conditions, primarily resonance frequency and wave amplification from the ground. We present local site parameters with their site geology for 37 sites using ambient noise data. Horizontal to vertical spectral ratio technique is used to estimate the spectral ratio curves. Based on the type of curve, sites are classified into four classes, viz. clear peak, broad peak, double and multi‐peak, and flat H/V curve. Sites seen with clear or broad peaks are located on either soil or weathered rocks, thus indicating large impedance contrast and sharp discontinuity with large velocity contrast. Multiple peaks are observed in either soil or boulder bed and reveal large impedance contrast, probably representing shallow and thick strata. Sites with flat curves are found on weathered/phyllite/granite gneiss/granite schist rock types within highly dissected hilly areas. Fourteen sites have a peak frequency >6 Hz with a dominance of broad and clear peaks in the Lesser and Higher Himalayan regions. On the contrary, foothills and part of Siwalik sites exhibited a peak frequency between 1.14 and 4.94 Hz. The results demonstrate that sites with thick soil cover and boulder bed areas, that is, Doon valley and foothills, show low‐frequency peaks and hard rock or shallow bedrock sites, that is, Lesser and Higher Himalaya exhibit a higher frequency range. The estimated H/V amplitude and peak frequency values have shown a good correlation with site geology and geomorphology.

Spectral Correlation Between the Non-uniform Input Ground Motion and the Dynamic Response of the Surrounding Rocks of a Long Tunnel

To generate several different time-history curves of ground motion, which have the ability to reflect local site effects, such as the traveling-wave effect and attenuation effect, for long circular tunnels, a random method for the synthesis of ground motion is employed. The dynamic response of the surrounding rocks of a long tunnel under the uniform and non-uniform input ground motions is analyzed using the vertical input method. Based on this, the spectral correlation between the input ground motion and the dynamic response of the surrounding rocks is investigated through the coherence function. Unlike the results under the uniform input ground motion, the transmission coefficient of the surrounding rock monitoring points of each section along the axial direction of the tunnel under the non-uniform input ground motion varies in the main frequency band. In addition, at the same frequency, the transmission coefficient of the monitoring points gradually increases along the tunnel’s axial direction, but the increasing magnitude is variable. The correlation function of each monitoring point along the tunnel axis under the non-uniform input ground motion generally decreases with frequency. Moreover, the further the distance from the tunnel entrance, the faster the attenuation of correlation. The maximum coherence coefficient and the axial distance of the tunnel are basically in conformity with the quadratic polynomial relationship. However, the maximum coherence coefficient of the non-uniform input ground motion is considerably greater than that of the uniform input ground motion. The gap increases with the distance, and the maximum gap is about 0.15.

The September 19th, 2017 Puebla, Mexico earthquake

This report presents the observations and findings following the 2017 Puebla earthquake that occurred inMexico on September 19th, 2017. The reconnaissance mission was a collaboration between the New ZealandSociety of Earthquake Engineering (NZSEE), the Universidad Autónoma Metropolitana (UAM) Azcapotzalco,the American Concrete Institute (ACI) Disaster Reconnaissance team, and the Colegio de Ingenieros Civilesde Mexico (CICM). During the earthquake, 77 buildings suffered partial or total collapse and more than8,000 buildings experienced damage ranging from slight damage to significant structural damage necessitatingdemolition. As observed in previous earthquakes, the unique soil conditions of Mexico City resulted inextensive damage to the city’s infrastructure, primarily due to local site effects. The earthquake causedrelatively more damage to buildings built on transition and soft soil zones (i.e. between hard and deep softsoils) than those on hard soils.The NZSEE and UAM team focussed on areas with widespread and extensive damage. They also assessedthe performance of repaired and retrofitted buildings after the 1985 Michoacán earthquake. It was found thatthe lessons learnt from the 1985 Michoacán earthquake led to some risk mitigation measures which benefitedseveral buildings in the 2017 earthquake. Retrofitted buildings were found to have performed very well withlittle or no damage when compared to other buildings.

Evaluation of a novel application of earthquake HVSR in site-specific amplification estimation

Ground response analyses (GRA) model the vertical propagations of SH waves through flat-layered media (1DSH) and are widely carried out to evaluate local site effects in practice. Horizontal-to-vertical spectral ratio (HVSR) technique is a cost-effective approach to extract certain site-specific information, e.g., site fundamental frequency (f0), but HVSR values cannot be directly used to approximate the levels of S-wave amplifications. Motivated by the work of Kawase et al. (2019), we propose a procedure to correct earthquake HVSR amplitudes for direct amplification estimations. The empirical correction compensates HVSR by generic vertical amplification spectra categorized by the vertical fundamental frequency (f0v) via k-means clustering. In this investigation, we evaluate the effectiveness of the corrected HVSR in approximating observed linear amplifications in comparison with 1DSH modellings. We select a total of 90 KiK-net (Kiban Kyoshin network) surface-downhole sites which are found to have no velocity contrasts below their boreholes and thus of which surface-to-borehole spectral ratios (SBSRs) can be taken as their empirical transfer functions (ETFs). 1DSH-based theoretical transfer functions (TTFs) are computed in the linear domain considering uncertainties in VS profiles through randomizations. Five goodness-of-fit metrics are adopted to gauge the closeness between observed (ETF) and predicted (i.e., TTF and corrected HVSR) amplifications in both amplitude and spectral shape over frequencies from f0 to 25 Hz. We find that the empirical correction to HVSR is highly effective and achieves a “good match” in both spectral shape and amplitude at the majority of the 90 KiK-net sites, as opposed to less than one-third for the 1DSH modelling. In addition, the empirical correction does not require a velocity model, which GRAs require, and thus has great potentials in seismic hazard assessments.

Towards understanding relationships between atmospheric pressure variations and long-period horizontal seismic data: a case study

SUMMARYVariations in atmospheric pressure have long been known to introduce noise in long-period (>10 s) seismic records. This noise can overwhelm signals of interest such as normal modes and surface waves. Generally, this noise is most pronounced on the horizontal components where it arises due to tilting of the seismometer in response to changes in atmospheric pressure. Several studies have suggested methodologies for correcting unwanted pressure-induced noise using collocated microbarograph records. However, how applicable these corrections are to varying geologic settings and installation types (e.g. vault versus post-hole) is unclear. Using coefficients obtained by solving for the residuals of these corrections, we can empirically determine the sensitivity of instruments in a specific location to the influences of pressure. To better understand how long-period, pressure-induced noise changes with time and emplacement, we examine horizontal seismic records along with barometric pressure at five different Global Seismographic Network stations, all with multiple broadband seismometers. We also analyse three Streckeisen STS-2 broadband seismometers, which are collocated with a microbarograph, at the Albuquerque Seismological Laboratory. We observe periods of high magnitude-squared-coherence (γ2-coherence; γ2 > 0.8) between the seismic and pressure signals which fluctuate through time, frequency, and even between seismic instruments in the same vault. These observations suggest that these tilt-generated signals are highly sensitive to very local (<10 m) site effects. However, we find that in cases where instruments are not located at a large depth (<100 m), the pressure-induced noise is polarized in a nearly constant direction that is consistent with local topographic features or the geometry of the vault. We also find that borehole instruments at a large depth (>100 m) appear to be unaffected by pressure-loading mechanisms outlined by Sorrells (1971) but possibly by Newtonian attraction. Correlating the induced-noise polarization direction with times of high coherence, we work to identify sensors that are ultimately limited by pressure-induced horizontal noise as well as period bands that can benefit from pressure corrections. We find that while the situation is complex, each sensor appears to have its own unique response to pressure. Our findings suggest that we can determine empirical relationships between pressure and induced tilt on a case by case basis.

Estimation of the moment magnitude and local site effects of a postulated Late Bronze Age earthquake: Mycenaean citadels of Tiryns and Midea, Greece

Previously interpreted archaeological and geological field data from the Argive Basin, Greece, have been used to hypothesized that the nearby Late Bronze Age Mycenaean citadels of Tiryns and Midea, which settled on bedrock, might record synchronized co-seismic structural damage due to earthquake ground-shaking at ca. 1190 BCE, the end of the Mycenaean palatial period. However, from a quantitative archaeoseismological perspective, this hypothesis has flaws: (a) it overlooks that several structures excavated in the undeformed Holocene sediments lack evidence of co- seismic structural damage and damage is only documented for sturdier structures within the citadels, (b) it leaves unexplained the moment magnitude of the ‘causative’ surface-rupturing earthquake, and (c) disregards the role of local site effects on surface ground-motion. The plausibility of the previously proposed earthquake hypothesis is tested by estimating the earthquake magnitude of the alleged ancient earthquake and its local site effects at and around the citadels, assuming that the earthquake truly occurred. A retrospective geotechnical site microzonation coupled with the calculation of seismic amplification factors, surface ground-motions, and earthquake intensity account for the local site effects assessment. The present numerical modeling results indicate that the citadels and contemporaneous adjacent structures of the peasants had a lower and higher seismic hazard, respectively. Seismic amplification factors, earthquake-induced ground shaking, and seismic intensity are indeed lower for Tiryns than for Midea. Therefore, these results refute the idea of seismically induced destruction of the citadels and challenge the plausibility of the earthquake hypothesis. The previously archaeologically documented destruction patterns unlikely represent physical evidence of co-seismic damage by the archaeologically proposed earthquake. Other explanations ought to be sought to elucidate the interpreted destruction pattern seen in these Mycenaean centers.

Simulation of the spatially correlated multiple-station earthquake ground motions of the coupled alluvial valley-hill terrain

Based on both the boundary element and spectral representation methods, an effective simulation method for multiple-station spatially correlated ground motions on both bedrock and surface is developed, incorporating the spectral density function, coherence function, and site transfer function that consider the wave scattering effect. The accuracy and feasibility of the present method is validated by a typical numerical example. Our results indicate that at the coupled alluvial valley-hill terrain, the presence of the mountain enlarges the ground motion of the alluvial valley significantly; the existence of alluvial valley enlarges the ground motion at the ridge of the mountain to some extent and weakens the ground motion at the top of the mountain. The local site conditions significantly affect the multipoint spatially correlated earthquake ground motions. It is necessary to use spatially varying ground motions with the rational consideration of local site effects as input during the seismic analysis of long-span structures

Strong ground motions from two moderate size (Mw5.5) Kachchh intraplate earthquakes, Gujarat, India

During 2006–2016, a strong motion seismic network of twenty 3-component accelerogarphs was deployed by the National Geophysical Research Institute, Hyderabad, India, in the epicentral region of the 2001 Mw7.7 Bhuj earthquake. On 7 March and 6 April 2006, two earthquakes of Mw5.5 have occurred in the Kachchh seismic zone, which led to an excellent dataset from 16 to 18 strong-motion accelerograph sites. This dataset enabled us to estimate strong motion parameters for these earthquakes that allowed us to examine the suitability of the design response spectra of BIS (criteria for earthquake-resistant design of structures, part I—general provisions and buildings, Bureau of Indian Standards, 2002) in Kachchh, Gujarat. Our study reveals that the estimated normalized response spectra at strong-motion accelerograph sites, which are lying in tertiary formations or near a zone of geological contact between Jurassic and tertiary formations, exceeded the design response spectra at 0.07–0.2 s, correlating with complete collapse of low-rise buildings, water tanks and dams in the area during the 2001 Bhuj earthquake. While the normalized acceleration spectrum of hard sediment (rock site) is found to not exceeding the design spectrum, correlating with the lack of damage in the Mesozoic hill zone. The estimated normalized acceleration spectra at SMA sites lying on hard sediments of Jurassic/Mesozoic formations are found to be lower than the design spectra, which suggests that these stations are less hazardous. We also notice that spectral acceleration values at few sites lying on quaternary formations have exceeded the design spectra at 3–4 s, suggesting these sites hazardous for engineered reinforced structures like bridges. Our estimated mean pseudo velocity spectra show peaks at 0.2, 0.5, 1.2 and 6 s. The peak at 6 s probably can cause damages to the reinforced engineered structures while the peak at 1.2 s could be causing damages to the multistoried reinforced buildings, as observed during the occurrence of the 2001 Bhuj mainshock. Thus, our estimated normalized acceleration spectra show peaks exceeding the design spectra at shorter (0.07–0.2 s, 0.5 s, 1–1.2 s) as well as longer periods (3–4 s, 6 s), which could be attributed to local site effects. We also notice that the modeled normalized response spectra for the shallow March event shows a better correlation with the NGA West2 model for tectonically active regions of US while the modeled normalized spectra for the deeper April event suggest a better correlation with the NGA east model for the stable parts of USA. We propose that the design spectra for the Kachchh region, Gujarat, India, should be modified incorporating local site, path and source effects.

Seismic hazard analysis and local site effect of the 2017 Mw 7.3 Sarpol-e Zahab, Iran, earthquake

A strong earthquake occurred on November 12, 2017, in Sarpol-e Zahab city, western Iran, with the moment magnitude ( $$M_{{\text{w}}}$$ ) of 7.3 and a focal depth of 18 km. The maximum horizontal peak ground acceleration of 0.69 g was recorded at the Sarpol-e Zahab station. Significant damages were observed in frame and masonry buildings, while the damage distribution was non-uniform throughout this small city. The preliminary site reconnaissance revealed that numerous engineering structures collapsed or considerably damaged in some regions, contrary with those non-structural masonry buildings in other regions which remained intact during earthquake. This paper represents a preliminary reconnaissance report prepared through the site visit done by the authors, a few days following the earthquake occurrence. Then, the data recorded by the strong ground motion stations in the affected city and the surrounding regions together with the geotechnical data gathered from the available boreholes in Sarpol-e Zahab are incorporated for probabilistic seismic hazard and local site effect analyses. The observed response spectra at two stations and distance-dependency of ground acceleration are compared with those predicted by some attenuation models. The results of probabilistic seismic hazard analysis in the return periods of 475 and 2475 years are compared with the observed ground response and the design spectra recommended by the Iranian seismic code (for site classes Types I and II). Several geotechnical boreholes from the previous works in the affected area were analyzed through the equivalent-linear site response approach in order to obtain the seismic response at the soil surface. The results are then compared with the code design spectra for the site classes of Types III and IV. It is demonstrated that the calculated response spectra are generally larger than those recommended by the Iranian seismic code, especially for the 4–7 stories buildings.

Influence of Local Site Condition on Vertical-to-Horizontal Spectrum Ratio – Insight from Site Response Analysis

ABSTRACT A vertical-to-horizontal (V/H) response spectral ratio of 2/3 is commonly adopted in earthquake engineering for assessing the magnitude of vertical motion. However, higher V/H ratios are found in some earthquake records. This study evaluates the factors that can influence the V/H ratio on the basis of vertical and horizontal site response analyses. Two sets of rock motions representing near-source and far-field conditions are propagated through four selected sites that vary in soil column thickness, groundwater table, soil type, and wave velocity profile. The V/H ratio on the ground surface is calculated and compared with that at the bedrock. Results show that the V/H ratio is amplified by the local site effect, and increases at low wave velocity and high intensity of input motion owing to the different nonlinearities presented in the vertical and horizontal directions. The groundwater table considerably varies the V/H ratio and should be considered in assessing the vertical motion or V/H ratio.

Joint modeling of Rayleigh wave dispersion and H/V spectral ratio using Pareto-based multiobjective particle swarm optimization

Estimating the shear wave velocity and thickness of geologic units in a sedimentary structure is important for quantifying the local site effect caused by an earthquake. Inversion of the Rayleigh wave dispersion alone is sensitive to the absolute average shear wave velocity, while the H/V spectral ratio is sensitive to velocity contrasts. The solution of these models in a joint system using conventional inversion techniques suffers from difficulties while evaluating partial derivatives, dependencies to the initial model that is sometimes difficult to estimate, and trapping at a local minimum. Herein, a joint model using the Pareto optimality technique with multiobjective particle swarm optimization was constructed as an effective global optimization method to decrease weakness and increase performance while estimating the depths and velocities. The presented approach is a multiobjective optimization method that does not require weighting, and allows evaluations of the individual objective function separately in a joint system. This study presents 2 synthetic joint system examples to account for a gradient-type and sharp velocity contrast cases, and an application from field data obtained from the Bursa Basin in Turkey. With these examples, an automated parameter search space was demonstrated to account for the abrupt velocity changes and a number of additional key points that are essential for a reasonable optimal solution.

Empirical Green’s Function Simulations Toward Site-Specific Ground Motion Prediction in Vietnam

Vietnam has a low-to-moderate seismicity, but the currently available strong ground motion data used as a basis for a seismic-resistant design are insufficient. Generally, to overcome this issue, strong ground motions recorded at other places around the world are used, which have similar seismic, tectonic and physical earthquake characteristics, such as earthquake magnitude, source model, distance to the source, tectonic geological conditions, and soil conditions. However due to different path effects and site effect, if applied to the site-specific studies in Vietnam, the above approach would generate certain errors. Therefore, it is important to obtain strong ground motion data that are applicable for seismic design of constructions in a particular region. Especially, it is important to adhere to strict seismic design requirements for facilities, such as hydropower, thermal, and nuclear power plants. One of the most interesting solutions is the theory of simulating the waveforms of strong earthquakes commonly known as the empirical Green’s function. The empirical Green’s function is a useful tool for estimating the ground motions produced by large earthquakes using small earthquake records. The basic idea of the method is that these small events data already incorporate the information of the propagation path and the local site effects. Ground-motion simulations essentially use these small events as an empirical Green’s function and add them following the scaling law based on the omega-square model. In this article, we simulate design basis ground motion for the Song Tranh 2 hydropower dam as an example. We have applied the empirical Green’s function method to predict broadband ground-motion time histories for several M5.5, one M5.7, and one M5.9 earthquake scenarios at the dam site based on M4.6 observed ground motions without/with considering radiation pattern corrections. The results confirm that strong ground-motion simulations are applicable to seismic hazard assessment in Vietnam. Once we obtain accurate source parameters, the site-specific synthetic ground motions of the earthquake scenarios can be used for seismic design safety in Vietnam.

Seismic Site Effect Mapping Based on Natural Frequency Using Microtremor Method in Sidoarjo District

Sidoarjo is one of the satellite districts of Surabaya. The regency has important infrastructures that support Surabaya as a big city, such as the airport, bus terminal, industrial estate and warehouses which are important to support the sustainability of the industries in Surabaya City and East Java Province. With its important role, Sidoarjo Regency faces the risk of disasters in the form of earthquakes caused by earthquake sources in the form of land faults. Faults located closest to the district of Sidoarjo are Blumbang Fault, Pasuruan Fault, Surabaya Fault, and Waru Fault. With this risk, a research is needed to determine the local site effects of land related to seismicity. Therefore, microtremor research was held in Sidoarjo Regency to determine the local site effect in the form of dominant frequency of the soil. Measurements were done in 37 points spread throughout the Sidoarjo Regency. With dominant frequencies mapping, an analysis of earthquake hazard levels were carried out due to geological factors around the Sidoarjo Regency. After measuring natural frequencies, the range of natural frequencies were found to be between 0.8 - 3.65 Hz. Low natural frequency values were found in Waru District and high frequencies were found in Sedati District.

Data-driven and machine learning identification of seismic reference stations in Europe

SUMMARYThe growing seismic networks and the increasing number of permanent seismic stations can help in improving the physical basis of seismic hazard assessment. For this purpose, the definition of reference site conditions is of great significance. If a reliable estimate of the reference ground motion is known, its modification at any given site can be modelled with respect to that reference site. Since the choice of a well-characterized reference site is not straightforward, mainly due to the high variability in the shallow layers, such choices prove to be affected by large uncertainties. While proxy parameters like the average S-wave velocity over the uppermost 30 m (vS30) might help in characterizing reference site conditions, such parameters are neither available at all sites nor do they allow concluding that the site is not affected by amplification and attenuation effects. In this study, we identify prospective reference sites across Europe in a harmonized and fully data-driven way. All analysis is based on freely available geological and geophysical data and no on-site measurements or site-specific proxies are required. The study accounts for both the influence of amplification and attenuation in a large frequency range. To address the key conceptual issues, we verify our classification based on machine learning techniques in which the influence of the individual site characterization parameters is investigated. Our study indicates that around 250 sites in Europe over more than 2000 investigated are not affected by local site effects and can de facto be considered as reference sites based on the criteria applied.

Local site effects evaluation by surface wave and H/V survey methods in Senirkent (Isparta) region, southwestern Turkey

This study aimed to investigate the site characterization of the Senirkent Basin (Isparta) by using the microtremor (H/V) and surface wave analysis (ReMi) methods. Senirkent district, which is located on the foothill of the Kapi Mountain, are prone to seismic and landslide hazards. After the last landslip disaster (1995), the city has continued to develop on the alluvial basin. The microtremor data collected at 41 stations were analyzed. The predominant frequency and the amplification of the soil were found to be in the range of 1.8–6.6 Hz and 0.8–6.8, respectively. These are 4.0–6.8 Hz and 1–2.5 around the slope of the Kapi Mountain and 0.8–3.6 Hz and 3.0–6.6 at alluvium deposits of the valley. The ReMi data collected along 41 profiles were analyzed to obtain a Vs30 map. The soil classifications were done by using Vs30 values according to NEHRP soil classification criteria. The results showed that the southern area of the study had better soil conditions with Vs30 between 360–1160 m/s and soil class between C and B. The alluvium deposits on the north are relatively low with Vs30 in the range of 260–360 m/s and soil class D.

Comparison of different local site effect estimation methods in site with high thickness of alluvial layer deposits: a case study of Babol city

During earthquake loading, seismic evaluation of site dynamical analysis is the most serious issue in geotechnical earthquake engineering. Seismic waves pass through soils and rocks to reach the ground surface; hence, their characters play an important role in surface strong ground motion parameters. There are numerous techniques for the estimation of local site effect. This study aims at the comparison of different local site effect estimation methods in Babol city, Iran, with high thickness of the alluvial layer (80 m). Babol strong motion records have been used in this study. The obtained results from strong ground motions data were compared with other methods. The results reveal that for a site with high thickness of alluvial layer deposits, the microtremor measurement method is the best way for estimating site effect. Moreover, the numerical site response analysis based on the International Building Code and National Earthquake Hazards Reduction Program may not provide accurate results for alluvial layers at deep solid foundation, where an obvious rock-soil interface cannot be detected within 30 m.

Research Status of 1-D Soil Layers Seismic Response

The local site effect of vibration propagation during earthquakes is usually considered by one-dimensional site response analysis, while the ground motion of the site is the result of the combined effect of the source, the propagation path and the local site conditions. In the study, the influence of ground motion input, soil layer properties and analysis methods need to be considered. Based on a large number of related literatures, this paper briefly summarizes the research status of seismic response of one-dimensional soil layer sites through the determination of bedrock ground motions, soil dynamic constitutive models, and analysis methods. In the future, the development of seismic response of soil sites is prospected and summarized.

Overview of local site effects and seismic microzonation mapping in Metropolitan Vancouver, British Columbia, Canada

A multi-year seismic microzonation project to map local variations of site response across Metropolitan (Metro) Vancouver, British Columbia, Canada, is currently underway. This paper presents our progress in one-dimensional site amplification hazard mapping of Metro Vancouver following our first field campaign. We initiated our microzonation study by assembling relevant geological, geophysical and geotechnical datasets from online and private sources to develop a regional 3D geodatabase. We perform site characterization near 20 strong-motion stations located on soft and stiff sediments using multiple non-invasive in situ seismic methods, including surface wave array and microtremor horizontal-to-vertical spectral ratio (MHVSR) techniques, to retrieve shear-wave velocity (Vs) depth profiles. We also compile all available earthquake recordings from 6 events of moment magnitude (M) > 3.9 to assess earthquake site amplification across Metro Vancouver. Comparison of the limited earthquake horizontal-to-vertical spectral ratio (EHVSR) data with MHVSRs demonstrates consistent empirical site amplification, supporting the use of MHVSRs as a valid proxy for earthquake site amplification in British Columbia. Vertical array recordings in soft sediments from a M 4.7 earthquake further demonstrate consistency between these amplification measures. To achieve spatial coverage for regional microzonation mapping, the same Vs profiling methods are applied in available open areas and more than 1100 MHVSR measurements are collected in a 600-m resolution grid. Three additional field campaigns will target validation of our non-invasive seismic methods with co-located invasive testing and fill in any spatial gaps. This paper summarizes the developed and applied methodologies and challenges encountered in seismic amplification hazard mapping for the Metro Vancouver region.