Empirical Attenuation Relationships Research Articles

Regional Arias Intensity Attenuation Relationship for Taiwan Considering VS30

The Arias intensity is a measure of earthquake intensity arrived at through the integration of a square of the acceleration time history. It has been demonstrated to be an effective predictor of earthquake damage potential in relation to short-period structures, liquefaction, and seismic slope stability, and has begun to be considered as a ground-motion measure suitable for use in probabilistic seismic hazard analysis (PSHA), as well as earthquake loss estimation. A new empirical Arias intensity attenuation relationship for shallow crustal earthquakes is developed where both fault type and a continuous site variable VS30 are considered. The relationship is based on a large number of strong-motion records (6570) from a wide range of earth- quake magnitudes (3.9-7.6) from the Taiwan Strong Motion Instrument Program (TSMIP) network. Its functional form is modified from that of Travasarou et al. (2003), which is derived from a point-source model, and the coefficients are determined through nonlinear regression analyses using a mixed-effects model. The results show that the incorporation of VS30 can significantly reduce regression error. The Arias intensity value predicted in the present study is generally similar to that obtained by Travasarou et al. (2003), but is different in detail, being more suitable for usage in PSHA for a tectonically young orogenic belt like that in Taiwan or New Zealand.

Modelling directivity of strong ground motion with a fractal, k−2, kinematic source model

The kinematic fractal source model presented in this study is able to simulate broad-band accelerograms with spectral amplitudes proportional to a fraction of the directivity coefficient Cd in the far-field approximation. This approach is based on a composite source description, where subevents are generated using a fractal distribution of sizes, and, by summation, produces k-square space distribution of the slip. Each elementary source is described as a crack-type slip model growing circularly from a nucleation point when the rupture front reaches it. In order to better control the directivity effect, the location of the nucleation point for an elementary source is assumed to be scale-dependent. For the larger sources, the nucleation point is located near the intercept of the crack with the rupture front, whereas for smaller sources, it is randomly chosen within the crack. For simplicity, a constant rupture velocity is assumed. Each subevent is set up with scale-dependent rise-time, assuming a boxcar source–time function, hence filtering out its own high frequency radiation. The resulting mean slip-velocity functions are very similar to the ones derived from dynamic rupture modelling. Ground motion synthetics are computed by convolving the slip-velocity functions with the Green's functions. It is demonstrated that, in the far-field approximation, accelerogram spectra follow the ω2 model with amplitudes controlled by the frequency-dependent directivity effects. In particular, spectral amplitudes at high-frequencies are proportional to a fraction of Cd. These results were verified for few earthquake magnitudes. In addition, a validation exercise was made in the near-fault region by modelling the complete wavefield of strong ground motion at a few receivers and for several rupture scenarios. The synthetic strong-motion parameters are compared to the ones predicted by empirical attenuation relationships. It is shown that calculated standard deviations are in good agreement with the empirical ones, as well as the ground-motion parameter amplitudes predicted as a function of distance for whole interval of source distance considered in modelling. Minor differences were found in peak ground-accelerations computed at large distance from the fault, a problem related to the simplified response of the medium.

CORRECTION-FACTOR MODEL OF RUPTURE DIRECTIVITY AND RADIATION PATTERN FOR EMPIRICAL GROUND-MOTION ATTENUATION RELATIONS OF CRUSTAL EARTHQUAKES

We present the concept of correction-factor model of rupture directivity and radiation pattern for empirical attenuation relations of peak ground velocity and acceleration response spectra. Approximate radiation pattern coefficients derived from accurate coefficients is used in this model. In addition, directivity function of bilateral line source by Boatwright (2007) based on directivity function of unilateral line source by Ben-Menahem (1961) is used in this model. The proposed correction-factor model for fault-normal and fault-parallel components has physically-based predictor variables and applicable to broadband distance from near-source to regional distance less than 200 km. We estimate regression coefficients of the model for strike-slip and dip-slip faultings using strong motion records of six crustal earthquakes with Mw>6.0 and verify the model by simulating the observed records.

History of Modern Earthquake Hazard Mapping and Assessment in California Using a Deterministic or Scenario Approach

Modern earthquake ground motion hazard mapping in California began following the 1971 San Fernando earthquake in the Los Angeles metropolitan area of southern California. Earthquake hazard assessment followed a traditional approach, later called Deterministic Seismic Hazard Analysis (DSHA) in order to distinguish it from the newer Probabilistic Seismic Hazard Analysis (PSHA). In DSHA, seismic hazard in the event of the Maximum Credible Earthquake (MCE) magnitude from each of the known seismogenic faults within and near the state are assessed. The likely occurrence of the MCE has been assumed qualitatively by using late Quaternary and younger faults that are presumed to be seismogenic, but not when or within what time intervals MCE may occur. MCE is the largest or upper-bound potential earthquake in moment magnitude, and it supersedes and automatically considers all other possible earthquakes on that fault. That moment magnitude is used for estimating ground motions by applying it to empirical attenuation relationships, and for calculating ground motions as in neo-DSHA (Zuccoloet al., 2008). The first deterministic California earthquake hazard map was published in 1974 by the California Division of Mines and Geology (CDMG) which has been called the California Geological Survey (CGS) since 2002, using the best available fault information and ground motion attenuation relationships at that time. The California Department of Transportation (Caltrans) later assumed responsibility for printing the refined and updated peak acceleration contour maps which were heavily utilized by geologists, seismologists, and engineers for many years. Some engineers involved in the siting process of large important projects, for example, dams and nuclear power plants, continued to challenge the map(s). The second edition map was completed in 1985 incorporating more faults, improving MCE’s estimation method, and using new ground motion attenuation relationships from the latest published results at that time. CDMG eventually published the second edition map in 1992 following the Governor’s Board of Inquiry on the 1989 Loma Prieta earthquake and at the demand of Caltrans. The third edition map was published by Caltrans in 1996 utilizing GIS technology to manage data that includes a simplified three-dimension geometry of faults and to facilitate efficient corrections and revisions of data and the map. The spatial relationship of fault hazards with highways, bridges or any other attribute can be efficiently managed and analyzed now in GIS at Caltrans. There has been great confidence in using DSHA in bridge engineering and other applications in California, and it can be confidently applied in any other earthquake-prone region. Earthquake hazards defined by DSHA are: (1) transparent and stable with robust MCE moment magnitudes; (2) flexible in their application to design considerations; (3) can easily incorporate advances in ground motion simulations; and (4) economical. DSHA and neo-DSHA have the same approach and applicability. The accuracy of DSHA has proven to be quite reasonable for practical applications within engineering design and always done with professional judgment. In the final analysis, DSHA is a reality-check for public safety and PSHA results. Although PSHA has been acclaimed as a better approach for seismic hazard assessment, it is DSHA, not PSHA, that has actually been used in seismic hazard assessment for building and bridge engineering, particularly in California.

Response spectral attenuation relations for in-slab earthquakes in Indo-Burmese subduction zone

From an analysis of a limited number of strong-motion data recorded in northeast Indian region, the in-slab earthquakes along the Indo-Burmese subduction zone are found to be characterized by much larger ground motion amplitudes than that for the earthquakes along other subduction zones around the world. Specific type of source, propagation path and site geologic condition may perhaps simultaneously be responsible for such anomalous behaviour. The empirical attenuation relations developed by Atkinson and Boore [3] using a global database for subduction zone earthquakes have been therefore suitably modified to be more appropriate for the northeast India. The modified relationships are developed by combining the data for both horizontal and vertical components of motion. The response spectra of the accelerograms recorded in northeast India from earthquakes with widely varying magnitude and distance are, in general, found to match very well with the predictions from the modified attenuation model. The proposed model can thus be used to obtain more realistic estimate of the contribution of in-slab subduction zone earthquakes to seismic hazard in the northeast Indian region.

ATTENUATION RELATIONS OF HORIZONTAL AND VERTICAL GROUND MOTIONS FOR INTRASLAB AND INTERPLATE EARTHQUAKES IN JAPAN

Vertical motions have been required as input motions to important structures, such as nuclear power plants and base-isolation structures. However, empirical attenuation relations of vertical motions for big intraslab and interplate earthquakes in Japan had not been proposed yet. Therefore in this study we develop attenuation relations for estimating horizontal and vertical ground motions caused by these earthquakes. The relations are provided for peak ground acceleration (PGA), peak ground velocity, and 5% damped acceleration response spectrum (SA) for radial, transverse, and vertical components. In order to use the relations as input motions we obtain site coefficients at bedrock with different S-wave velocities. The attenuations of horizontal motions in this study obtained from records observed at the fore-arc are smaller than those in the previous ones. The ground motions for big intraslab and interplate earthquakes occurring at the Pacific plate are larger than those at the Philippine Sea plate at most cases. We find that the PGA and the SA in a short period range for intraslab earthquake are larger than those for interplate earthquakes at the same focal depth D and are roughly proportional to D2/3.

Fast assessment of earthquake loss and its application to the 2008 MS8.0 Wenchuan earthquake

The paper introduces firstly the seismic loss assessment method based on macro-economic indicators and new vulnerability models determined by the data from the on-site damage and loss survey to earthquakes occurred in China during the last two decades. The fast assessment for the 2008 Wenchuan earthquake with MS8.0 is given based on an empirical intensity attenuation relationship. Compared with the assessment based on the practical seismic intensity map of the event according to the on-site investigation, the result demonstrates the usability of the seismic vulnerability models introduced in the paper. In addition, it is indicated that the main uncertainty of losses in the fast loss assessment comes from the uncertainty of the estimation of seismic ground motion.

Integrating RS technology into a GIS-based earthquake prevention and disaster reduction system for earthquake damage evaluation

This paper presents a method to integrate remote sensing (RS) data processing, generation of isoseismal lines and human-computer interaction modules into an improved GIS-based disaster reduction system. Using the RS data processing module, a statistical sample gray value and the RS-intensity at each field survey point in the region are calculated from the probabilistic relationship between the RS-variable and earthquake intensity, and stored in the GIS-based system database. Then, isoseismal lines are generated by a trend surface model from RS-intensity. They are further improved via modification of the isoseismal lines based on the empirical attenuation relationship calculated by using the RS-variable in the human-computer interaction module. The field survey shows that the proposed method gives a good generation of isoseismic lines. As a result, the accuracy of the damage and loss evaluation and the efficiency of the emergency decision making capability are improved.

Empirical Attenuation Relationships for Western Anatolia, Turkey

Seismic hazard studies have become progressively more important for earthquake engineering applications in western Anatolia, which contains one of the world’s best examples of a rapidly extending intra-continental tectonic regime. A two-stage regression analysis was applied to peak ground acceleration and 5%-damped spectral acceleration values of 168 recordings from 49 earthquakes in order to develop empirical attenuation relationships which can be used to predict ground motion for western Anatolia. Moment magnitudes for earthquakes range between 4.0 and 6.4 while the hypocentral distances range between 15 and 200 km in our dataset. Site classifications, as one of the predictor variables for the regression analysis, were obtained using horizontal to vertical spectral ratio estimates. These estimates, together with empirical attenuation relationship predictions, have shown that soil amplification is significant in western Anatolia. Attenuation relationship models that are obtained explicitly account for nonlinear sediment effects for deep soil sites in the region. Nonlinear effects of deep soil sites at lower periods are significant at the higher levels of shaking and manifest over-prediction for acceleration values, while they manifest lower prediction values at lower levels of shaking. Both results from the horizontal to vertical ratio method and the regression analysis show that the number of strong motion stations located on the rock sites in the region should be increased and the present site classification of strong motion stations in Turkey should be re-evaluated in detail. When obtained attenuation relation models were compared with the attenuation relationships based on data from tectonically similar regions, the attenuation relations modelled for a specific region could not, in general, be used in engineering applications realized for another region. Our results also indicate that the spectral acceleration model defined in the Turkish Building Code cannot adequately explain magnitude and distance dependencies in western Anatolia.

Near-Source Ground Motion along Strike-Slip Faults: Insights into Magnitude Saturation of PGV and PGA

Empirical data suggest that peak ground acceleration (PGA) and peak ground velocity (PGV) saturate as a function of magnitude for large magnitude ruptures close to the fault. Because data are sparse in the near-source region of large magnitude events, we have explored this question by simulating large magnitude strike-slip earthquakes. We use kinematic simulations to generate ground motion for a strike-slip fault that has a large aspect ratio (length/width). We consider both homogeneous or heterogeneous rupture models. We find that close to the fault along strike profiles of PGV and PGA increase to a maximum at a certain epicentral distance and then decrease to an asymptotic level beyond this distance. Critical factors for predicting ground motion are the position of an observer along strike, the depth of the hypocenter below the top of the fault, and the ratio of rupture velocity to shear-wave velocity. To understand the cause of the amplitude variation of along strike profiles of PGV and PGA, we use the isochrone method and the concept of the critical point to investigate how the geometry and kinematic parameters interact to produce the computed ground motion. We construct a predictor based on the critical point that does well in predicting the position of the maximum of PGV and PGA for stations close to the fault. For heterogeneous rupture models we find that the behavior is more complex though the general observation that along strike profiles of PGV and PGA increase to a maximum and then decrease still holds. This has implications for empirical attenuation relationships that essentially average the ground motion for all stations along strike with the same distance to the fault.

Probabilistic modeling of seismically triggered landslides using Monte Carlo simulations

The 2004 Chuetsu earthquakes of Niigata (Japan) triggered numerous landslides, and the most widespread types of landslides were highly disrupted, relatively shallow slides and soil (debris) flows. This paper presented a method to evaluate slope instability using Newmark displacement on a pixel-by-pixel basis in a given area. The proposed method was able to integrate Newmark displacement modeling and Monte Carlo simulations within geographical information systems. In the modeling, an empirical attenuation relationship was utilized to calculate Arias intensity over this study area, and the variability of geotechnical parameters was taken into account to calculate coseismic landslide displacement. Before deriving the displacement from related inputs, the Monte Carlo simulations ran 1,500 times and generated 1,500 displacement values for each grid cell, and then means and standard deviations of displacement were calculated and probabilistic distributions can be obtained. Finally, given 10 cm as a threshold value of displacement, estimated probabilities of displacement exceeding 10 cm were shown as a map of seismic landslide hazards. The resulting hazard map was classified into four categories from very low to high level.

Seismic Hazard of Hong Kong

This paper reviews the probabilistic seismic hazard assessment studies undertaken in recent years to estimate the potential seismic ground motion levels on bedrock in Hong Kong. A detailed catalogue of historical and recent seismicity within the South China region has been compiled. A suite of published empirical and stochastic attenuation relationships have been used with alternative source models and source parameters in a logic tree hazard analysis. Uniform hazard bedrock ground-motion spectra having various probabilities of being exceeded in 50 years have been calculated. The results have been de-aggregated to investigate what earthquake magnitude and distance combinations have contributed most to the hazard levels for the different probabilities and structural periods. The obtained uniform hazard spectra have been compared to the study using an alternative assessment approach developed by the University of Hong Kong. Recent recorded earthquake ground motions in Hong Kong are also presented with the uniform hazard spectra.

Site Classification Assessment for Estimating Empirical Attenuation Relationships for Central-Northern Italy Earthquakes

The aim of this article is to investigate the ground motion attenuation of the most industrialized and populated regions of Italy, evaluating the capability of different approaches to estimate site dependent models. The 5.2 local magnitude earthquake on November 24, 2004 shocked the areas of Northern Italy producing damage of about 215 million euros. The data set, including 243 earthquakes of local magnitude up to 5.2, has been collected in the period December 2002–October 2005 by 30 three-component seismic stations managed by Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Milano (INGV-MI). Empirical attenuation relationships have been estimated for horizontal peak ground velocity (PGHV), acceleration (PGHA), displacement (PGHD), and for response spectral acceleration (SA) for periods between 0.1 and 1.5 s. To estimate suitable attenuation models, in particular for sites characterized by thick sedimentary geological formations, a soil discrimination based on EU8 code can lead to wrong evaluations. On the contrary, a classification based on H/V spectral ratios of seismic ambient noise (NHV) allows the models to fit better real and predicted data and to reduce the uncertainties of the process. For each receiver, NHV have been strengthened by additional H/V spectral ratio of earthquake data (EHV), calculated considering different portions of the analysed signals. In order to validate the PGHA attenuation relationship for greater magnitudes, accelerometric records, relative to Central-Northern Italy strong motions occurring in the last 30 years, have been collected and superimposed to our attenuation curves.

Ground motion models for the Molise region (Southern Italy)

The aim of this paper is to evaluate empirical attenuation relationships in order to validate peak values and pseudo-velocity spectra to calibrate shaking scenarios for the Molise area, which was struck by two earthquakes of M w=5.7 (INGV-Harvard European-Mediterranean Regional Centroid-Moment tensor project) on October 31st and November 1st, 2002. Before the earthquake occurrence this region was classified as not hazardous, according to the former Italian seismic code. After the main-shocks, felt in many towns of the Molise and Puglia regions, a strong motion and a seismic temporary network were installed in the epicentral area and surrounding regions. This allowed the collection of a large data set, useful to characterize this area. The joint velocity-acceleration data set has been used to derive ground motion models for peak ground acceleration, peak ground velocity, and pseudo-velocity response spectra for both maximum horizontal and vertical components of the motion. The results obtained for the Molise area have been compared with the attenuation pattern of the Umbria-Marche region (central Italy) and the Italian territory. Remarkable differences have been observed leading to a discussion of the possible regional dependence of ground motion.

Ground-Motion Predictions from Empirical Attenuation Relationships versus Recorded Data: The Case of the 1997-1998 Umbria-Marche, Central Italy, Strong-Motion Data Set

We evaluate the goodness of fit of attenuation relations commonly used for the Italian national territory (Sabetta and Pugliese, 1996) by using the maximum likelihood approaches of Spudich et al. (1999) and Scherbaum et al. (2004). According to the classification scheme proposed by Scherbaum et al. (2004), the Sabetta and Pugliese (1996) relationships show consistent discrepancies between the predicted and the observed peak ground acceleration (pga) at rock sites in the Umbria- Marche region, central Italy; however, at soft sites the agreement between observations and prediction is satisfactory. The bias of the residuals, computed with the Sabetta and Pugliese (1996) models for pga, peak ground velocity, (pgv) and pseudovelocity response spectrum (psv) (for M l = 4–6 and epicentral distances up to 100 km) is negative. This means that on the average, the predictions overestimate the observations, but the overestimation decreases with increasing magnitude. Then, we present regional predictive relations (UMA05) for maximum horizontal pga, pgv, and 5%-damped psv, derived from the strong-motion data recorded in the Umbria-Marche area and classified as to four site categories. The UMA05 attenuation relationships for rock sites are log 10 (PGA) = −2.487 + M 1 − 1.280 log 10 ( R 2 + 3.94 2 ) 0.5 ± 0.268 log 10 (PGV) = −1.803 + 0.687 M 1 − 1.150 log 10 ( R 2 + 2.74 2 ) 0.5 ± 0.300 and log 10 (PGA) = −2.500 + 0.544 M 1 − 1.284 log 10 R h ± 0.292 log 10 (PGV) = −1.752 + 0.685 M 1 − 1.167 log 10 R h ± 0.297, where pga is measured in fraction of g and pgv in centimeters per second, M l is the local magnitude in the range 4–6, R is the epicentral distance in the range 1–100 km, and R h is the hypocentral distance in kilometers. We used the random effect model (Brillinger and Priesler, 1985; Abrahamson and Youngs, 1992; Joyner and Boore, 1993; Joyner and Boore, 1994) to estimate the component of variance related to the earthquake-to-earthquake, station-to-station, and record-to-record variability, and to quantify the benefit of introducing a site classification in the attenuation model to reduce the variance. The introduction of the site classification in the attenuation model allows a reduction of the station-to-station component of variability (from 0.19 to 0.14 for pga, and from 0.21 to 0.18 for pgv). We also found that the record- to-record component represents the largest contribution to the model uncertainty.

Probabilistic Analysis of Tsunami Hazards*

Determining the likelihood of a disaster is a key component of any comprehensive hazard assessment. This is particularly true for tsunamis, even though most tsunami hazard assessments have in the past relied on scenario or deterministic type models. We discuss probabilistic tsunami hazard analysis (PTHA) from the standpoint of integrating computational methods with empirical analysis of past tsunami runup. PTHA is derived from probabilistic seismic hazard analysis (PSHA), with the main difference being that PTHA must account for far-field sources. The computational methods rely on numerical tsunami propagation models rather than empirical attenuation relationships as in PSHA in determining ground motions. Because a number of source parameters affect local tsunami runup height, PTHA can become complex and computationally intensive. Empirical analysis can function in one of two ways, depending on the length and completeness of the tsunami catalog. For site-specific studies where there is sufficient tsunami runup data available, hazard curves can primarily be derived from empirical analysis, with computational methods used to highlight deficiencies in the tsunami catalog. For region-wide analyses and sites where there are little to no tsunami data, a computationally based method such as Monte Carlo simulation is the primary method to establish tsunami hazards. Two case studies that describe how computational and empirical methods can be integrated are presented for Acapulco, Mexico (site-specific) and the U.S. Pacific Northwest coastline (region-wide analysis).

Empirical-Stochastic Ground-Motion Prediction for Eastern North America

An alternative approach based on a hybrid-empirical model is utilized to predict the ground-motion relationship for eastern North America (ENA). In this approach, a stochastic model is first used to derive modification factors from the ground motions in western North America (WNA) to the ground motions in ENA. The ground-motion parameters are then estimated to develop an empirical attenuation relationship for ENA using empirical ground-motion relationships from WNA .W e develop an empirical-stochastic source model for both regions to obtain ground mo- tions at different magnitude-distance range of interest. At short distances (R 30 km) and large magnitudes (Mw 6.4), an equivalent point-source model is carried out to consider the effect of finite-fault modeling on the ground-motion parameters. Source focal depth and Brune stress drop are assumed to be magnitude dependent. We choose three well-defined empirical attenuation relationships for WNA to com- pare the empirical ground-motion processes between the two regions. A composite functional attenuation form is defined, and, in turn, a nonlinear regression analysis is performed by using a genetic algorithm (GA) for a wide range of magnitudes and distances to develop an empirical attenuation relationship from the stochastic ground- motion estimates in ENA. The empirical-stochastic attenuation relationship for hor- izontal peak ground acceleration and spectral acceleration are applicable to earth- quakes of Mw 5.0-8.2 at distances of up to 1000 km. The resulting attenuation model developed in this study is compared with those used in the 2002 national seismic hazard maps, derived in the 2003 Electric Power Research Institute studies and re- corded in ENA. The comparison of the results to the other attenuation functions and the available ENA data show a reasonable agreement for the ENA ground motions.

Macrospatial Correlation Model of Seismic Ground Motions

It is very important to estimate a macrospatial correlation of seismic ground motion intensities for earthquake damage predictions, building portfolio analyses etc., whereby damage in different locations has to be taken into account simultaneously. This study focuses on spatial correlation of the residual value between an observed and a predicted ground motion intensity, which is estimated by an empirical mean attenuation relationship. The residual value is modeled in such a way that the joint probability density function (PDF) of seismic ground-motion intensity can be characterized by the spatial correlation model as well as an empirical mean attenuation relationship, assuming that it constitutes a homogeneous two-dimensional stochastic field. Using the dense observation data of earthquakes that occurred in Japan and Taiwan in recent years, the macrospatial correlation model is proposed and the assumption of homogeneity is verified in this paper.

Response to the discussion: Discussion of the paper “An empirical attenuation relationship for northwestern Turkey ground motion using a random effects approach”

Response to the discussion: Discussion of the paper “An empirical attenuation relationship for northwestern Turkey ground motion using a random effects approach”

Discussion of the paper ‘An empirical attenuation relationship for Northwestern Turkey ground motion using a random effects approach’

Ozbey et al. [1] have worked out a new attenuation relationship applicable to northwestern Turkey based on recent ground motion data recorded during the 1999 Turkey earthquakes and a few of their following events. Because of our own work along similar lines [2,3] we believe the evolution of ground motion predictions for the same or similar regions is of interest even though our own models are intended to be applicable to the whole of Turkey. Ground motion predictions based on records made in Turkey are affected by two influences. One is the relative uncertainty that shrouds the local site character. A good many sites do not have borehole or other data to establish their local site descriptor. The other is the interference from the buildings where the sensor may have been placed. In spite of these shortcomings, we have utilized available data from 47 stations that recorded 93 horizontal components during 19 distinct events to report prediction expressions in [2]. We have now updated this study by considering 57 earthquakes during 1976–2003 containing 112 records with 223 horizontal acceleration time series, to be reported in [3]. In 1999, Kocaeli earthquake data comprises 46 and 35% of our database assembled in [2,3], respectively. Ozbey et al. is based on 17 earthquakes that occurred within a one-year time