Attenuation Relationships Research Articles

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.

A Comparative Study of the Least Squares Method and the Genetic Algorithm in Deducing Peak Ground Acceleration Attenuation Relationships

In engineering applications, the development of attenuation relationships in a seismic hazard analysis is a useful way to plan for earthquake hazard mitigation. However, finding an optimal solution is difficult using traditional mathematical methods because of the nonlinearity of many relationships. Furthermore, using unweighted regression analysis in which each recording carries an equal weight is often problematic because of the non-uniform distribution of the data with respect to distance. In this study, the least squares method (LSM) and a genetic algorithm (GA) were employed as optimization methods for an attenuation model to compare the robustness and prediction accuracy of the two methods. Different (equal and unequal) weights of each recording were used to compare the adaptability of the weighting for practical application. The unequal weights of each recording were defined as functions of the hypocentral distance or the shortest distance from a station to the fault on the earth’s surface. Finally, regression analysis of horizontal peak ground acceleration (PGA) attenuation model in southwest Taiwan was shown.

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.

Preface to the Special Issue on Potential Geohazards of the Taipei Metropolitan Area

The Taipei metropolitan area is located within a complex tectonic environment where several types of geohazards may readily occur. In order to better characterize and understand the tectonic environment and related surface processes that may threaten the residents of Taipei, the Taiwan Central Geological Survey launched a then newly integrated project a few years ago aimed at gathering up-todate tectonic, volcanic, seismic, geologic and geochemical data in the northern and offshore Taiwan. Many new and exciting findings have arisen from such a program and have provided further insight into the overall sources of geologic and seismic hazards around the Taipei metropolitan area. Earthquake threats for the Taipei metropolitan area come from several potential sources, including large earthquakes with epicenters located some distance from Taipei for example, the 921 Chi-Chi earthquake and earthquakes occurring offshore Hualien. If certain crustal conditions develop at the plate interface underneath the Taipei Basin and allow a reflection of seismic waves into the Taipei region, earthquakes can cause severe surface vibration resulting in serious damage. Another possible earthquake threat comes from fault activities at shallow depths such as the Shanchiao normal fault. Because most of the Taipei metropolitan area is located upon the soft Quaternary sediments of the geometrically complex Taipei Basin, it is important to better understand the physical properties of the basin sediment for seismic wave propagations. Several papers in this special issue address related issues of seismic wave properties and site responses in the Taipei metropolitan area. Furthermore, active volcanoes may also result in serious damage to society and surrounding environs as documented by numerous hazardous eruptions worldwide. Although no historical volcanic eruptions have been recorded in the Taiwan region, empirical and phenomenal evidence indicates that the Tatun volcano group and the Kueishantao volcanic island may include active volcanoes raising the critical question of how to evaluate the activities and threats of the volcanoes in Tatun and Kueishantao. Several papers address these questions in this issue to better characterize the status of volcanic activities and underlying processes. Here: Chen et al. (2010b) examine Holocene activities of the Shanchiao Fault by compiling sedimentary records, particularly depositional facies and available age dates of three boreholes in the Taipei Basin. The depositional history of the Taipei Basin since the Last Glacial Maximum can be quite well reconstructed using a simple back-stripping method. They point out tectonic subsidence events that may possibly be related to major earthquakes and suggest further studies of the fault activities are needed to explore other possibilities of earthquake events. Here Cheng et al. (2010) use available data to evaluate probabilistic seismic hazards including the attenuation relationship of the peak ground acceleration, fault-slip data, and seismicity. Important earthquake sources are pointed out in the metropolitan Taipei area. In addition to the long return earthquake period of active faults, the study calls for attention to the threats of high peak acceleration resulting from subduction zone earthquakes beneath the Taipei area. Recent surface deformation and changes may be monitored by new satellite-borne and airborne remote sensing techniques, particularly InSAR and LiDAR. Chang et al. (2010a) apply DInSAR and PSInSAR techniques to analyze the general uplift and subsidence pattern in northern Taiwan and show regions of surface change of the past decade as related to fault activities. Meanwhile, Chang et al. (2010b) present the mapping results of the Nankan lineament, which is considered to be an active fault as outlined by the Taiwan Central Geologic Survey, using the newly-derived airborne LiDAR topographic data and concludes that the lineament has not been tectonically active since the deposition of the alluvial fans, thus posing less threat to the Taipei area. Huang et al. (2010a) reconstruct two-dimensional motions of the magnitude 7.1 earthquake that occurred offshore eastern Taiwan in 2002 based on 89 free-field strong motion records in northern Taiwan. According to the study, seismic wave amplifications are obvious within the Taipei Basin, especially where the sediment is the thickest. Studying the same earthquake, Huang et al. (2010c) find that seismic waves travel within the Taipei Basin and have been reflected back from its western edge with a dominant frequency of about one Hz. Characterization of these seismic waves within the Taipei Basin should provide further information for prevention of shaking-induced hazards and importantly more realistic modeling of seismic propagation. Terr. Atmos. Ocean. Sci., Vol. 21, No. 3, I-III, June 2010

Protective performance and protective mechanism of SiO2 aerogel under explosive loading

The propagation character of shock wave in SiO2 aerogel under explosive loading is studied using a polyvinylidene fluoride piezoelectric sensor. The propagation character of shock wave in aluminum foam is also determined for comparison. The results show that the peak stress of the shock wave follows the exponential attenuation relation with the propagation distance of the shock wave in SiO2 aerogel. The shock wave attenuates more obviously in SiO2 aerogel than in aluminum foam. The special nano-porous network structure of SiO2 aerogel results in better attenuation effect of shock wave in aerogel. The shock wave velocity in SiO2 aerogel is extremly low, thus the chase of the unloading wave leads to the further attenuation of shock wave.

Analysis of strong ground motions to evaluate regional attenuation relationships

Italian attenuation relationships at regional scale have been refined using a data set of 322 horizontal components of strong ground motions recorded mainly during the 1997-1998 Umbria-Marche, Central Italy, earthquake sequence. The data set includes records generated by events with local magnitude (M L ) ranging between 4.5 and 5.9, recorded at rock or soil sites and epicentral distance smaller than 100 km. Through a multiple step regression analysis, we calculated empirical equations for the peak ground acceleration and velocity, the Arias Intensity and for the horizontal components of the 5% damped velocity pseudo response spectra, corresponding to 14 frequencies ranging from 0.25 to 25 Hz. We compared our results with well known predictive equations, widely used on the national territory for Probabilistic Seismic Hazard Analysis. The results obtained in this study show smaller values for all the analyzed ground motion indicators compared to other predictive equations.

Seismic hazard assessment for the Sofia area

The capital of Bulgaria, Sofia, is situated in the center of the so-called Sofia area. This is the most populated industrial and cultural region of Bulgaria that faces considerable earthquake risk. We apply a version of machine code EQRISK for hazard assessment of the Sofia area according to the Cornell-McGuire approach. The probabilistic seismic hazard analysis is based on a simplified seismogenic model, which is derived from seismic zoning of Bulgaria. We show, using a Monte Carlo approach, that uncertainties in seismic input have a relatively small effect on the PSHA output, especially when compared with uncertainties associated with the attenuation relationship. Our PSHA map shows that a 10–3 annual probability of the PGA exceeds 0.3 g in much of the Sofia area

Uncertainty analysis for seismic hazard in Northern and Central Italy

In this study we examine uncertainty and parametric sensitivity of Peak Ground Acceleration (PGA) and 1-Hz Spectral Acceleration (1-Hz SA) in probabilistic seismic hazard maps (10% probability of exceedance in 50 years) of Northern and Central Italy. The uncertainty in hazard is estimated using a Monte Carlo approach to randomly sample a logic tree that has three input-variables branch points representing alternative values for bvalue, maximum magnitude (Mmax) and attenuation relationships. Uncertainty is expressed in terms of 95% confidence band and Coefficient Of Variation (COV). The overall variability of ground motions and their sensitivity to each parameter of the logic tree are investigated. The largest values of the overall 95% confidence band are around 0.15 g for PGA in the Friuli and Northern Apennines regions and around 0.35 g for 1-Hz SA in the Central Apennines. The sensitivity analysis shows that the largest contributor to seismic hazard variability is uncertainty in the choice of ground-motion attenuation relationships, especially in the Friuli Region (?0.10 g) for PGA and in the Friuli and Central Apennines regions (?0.15 g) for 1-Hz SA. This is followed by the variability of the b-value: its main contribution is evident in the Friuli and Central Apennines regions for both 1-Hz SA (?0.15 g) and PGA (?0.10 g). We observe that the contribution of Mmax to seismic hazard variability is negligible, at least for 10% exceedance in 50-years hazard. The overall COV map for PGA shows that the uncertainty in the hazard is larger in the Friuli and Northern Apennine regions, around 20-30%, than the Central Apennines and Northwestern Italy, around 10-20%. The overall uncertainty is larger for the 1-Hz SA map and reaches 50- 60% in the Central Apennines and Western Alps.

A probabilistic seismic hazard assessment for Greece and the surrounding region including site-specific considerations

A probabilistic approach was applied to map the seismic hazard in Greece and the surrounding region. The procedure does not require any specification of seismic sources or/and seismic zones and allows for the use of the whole seismological record, comprising both historical and instrumental data, available for the region of interest. The new seismic hazard map prepared for Greece and its vicinity specifies a 10% probability of exceedance of the given Peak Ground Acceleration (PGA) values for shallow seismicity and intermediate soil conditions for an exposure time of 50 years. When preparing the map, the new PGA attenuation relation given by Margaris et al. (2001) was employed. The new map shows a spatial distribution of the seismic hazard that corresponds well with the features of shallow seismicity within the examined region. It depicts the level of seismic hazard in which the exceedance of the PGA value of 0.25 g may be expected to occur within limited areas. The highest estimated levels of seismic hazard inside the territory of Greece are found in the Northern Sporades Islands, where PGA values in excess of 0.50 g are reached at individual sites, and in the Zante Island in Western Greece, where PGA values in the range of 0.35 g to 0.40 g are obtained at more numerous localities. High values are also observed in the sea between the Karpathos and Rhodes islands, near the Island of Amorgos (Cyclades Archipelago) and in the Southwestern Peloponnesus. The levels of seismic hazard at the sites of seven Greek cities (Athens, Jannena, Kalamata, Kozani, Larisa, Rhodes and Thessaloniki) were also estimated in terms of probabilities that a given PGA value will be exceeded at least once during a time interval of 1, 50 and 100 years at those sites. These probabilities were based on the maximum horizontal PGA values obtained by applying the design earthquake procedure, and the respective median values obtained were 0.24 g for Athens, 0.28 g for Jannena, 0.30 g for Kalamata, 0.21 g for Kozani, 0.24 g for Larisa, 0.43 g for Rhodes and 0.35 g for Thessaloniki. The probabilities of exceedance of the estimated maximum possible PGA value were also calculated for the cities to illustrate the uncertainty of maximum PGA assessment.

Strong ground motion attenuation in Aswan area, Egypt

Recent and paleo seismicity indicate that moder- ate seismic activity is relatively large for Aswan area. This is a warning on the possibility of occurrence of earthquakes in the future too. No strong motion records are available in Aswan area for engineers to rely upon. Consequently, the seismological modeling is an alternative approach till sufficient instrumental records around Aswan become available. In the present study, we have developed new ground motion attenuation relationship for events spanning 4.0≤Mw≤7.0 and distance to the surface projection of the fault up to 100 km for Aswan based on a statistically simulated seismological model. We generated suites of ground motion time histories using stochastic technique. The ground motion attenuation relation describes the dependence of the strength of the ground motions on the earthquake magnitude and distance from the earthquake. The proposed equation for peak ground acceleration (PGA) for the bed rock is in the form of: log PGA=gal ðÞ ¼ 1:24 þ 0:358 Mwlog R ðÞ �0:008R þ 0:22P.W here PGA is the peak ground acceleration in gal (cm/s 2 ); Mw, its moment magnitude; R is the closest distance between the rupture projection and the site of interest; and the factor P is a dummy variable. It is observed that attenuation of strong motion in Aswan is correlated with those used before in Egypt.

PROBABILISTIC SEISMIC HAZARD ASSESSMENT FOR THE DEMOCRATIC REPUBLIC OF CONGO AND SURROUNDING AREAS

Research Article| December 01, 2009 PROBABILISTIC SEISMIC HAZARD ASSESSMENT FOR THE DEMOCRATIC REPUBLIC OF CONGO AND SURROUNDING AREAS T. MAVONGA; T. MAVONGA University of the Witwatersrand, Private Bag 3, WITS, 2050 South Africa. Goma Volcanic Observatory, 142 Rond Point Avenue, Goma, North Kivu, Democratic Republic of the Congo, e-mail: mavotulu@gmail.com Search for other works by this author on: GSW Google Scholar R.J. DURRHEIM R.J. DURRHEIM University of the Witwatersrand, Private Bag 3, WITS, 2050 South Africa, Council for Scientific and Industrial Research, PO Box 91230, Auckland Park, 2006, South Africa, e-mail: raymond.durrheim@wits.ac.za Search for other works by this author on: GSW Google Scholar South African Journal of Geology (2009) 112 (3-4): 329–342. https://doi.org/10.2113/gssajg.112.3-4.329 Article history first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation T. MAVONGA, R.J. DURRHEIM; PROBABILISTIC SEISMIC HAZARD ASSESSMENT FOR THE DEMOCRATIC REPUBLIC OF CONGO AND SURROUNDING AREAS. South African Journal of Geology 2009;; 112 (3-4): 329–342. doi: https://doi.org/10.2113/gssajg.112.3-4.329 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 SocietySouth African Journal of Geology Search Advanced Search Abstract A probabilistic approach was used to map the seismic hazard in Democratic Republic of Congo and surrounding areas, and assess the seismic hazard level for 14 cities in the region. Seismic hazard maps for 2%, 5% and 10% chance of exceeding the indicated ground accelerations in 50 years were prepared using a homogenised 90-year catalogue compiled for moment magnitudes; the attenuation relations of Mavonga (for the Western Rift Valley of Africa), Jonathan (for eastern and southern Africa) and Atkinson and Boore (for eastern North America); and the EZ-Frisk software package. The highest levels of seismic hazard were found in the Lake Tanganyika Rift seismic zone, where peak ground accelerations in excess of 0.32 g, 0.22 g and 0.16 g are expected to occur with 2%, 5% and 10% chance of exceedence in 50 years, respectively. The seismic hazard in the Congo Basin diminishes with distance away from the Western Rift Valley until, at a distance of about 450 km, the chance of exceeding 0.05 g (the threshold value of engineering interest) is less than 10% in 50 years. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Estimating Magnitude and Location of Alaskan Earthquakes Using Intensity Data

Abstract I have developed relationships describing the attenuation of Modified Mercalli Intensity (MMI) with distance for three regions of Alaska (south-central, interior, and southeast). The sparse intensity data precluded development of site-specific corrections similar to those determined in other regions of the United States. I tested the intensity attenuation relationships on sets of calibration events, events with well-determined locations and instrumentally determined magnitudes, for south-central and interior Alaska (sufficient events were not available for the southeast region). My comparisons indicate the attenuation relationships gave event intensity centers within 50 to 60 km of event epicenters and magnitude estimates within 0.35 to 0.44 magnitude units of instrumentally determined magnitude. I then used these attenuation relationships to analyze historic earthquakes occurring between 1899 and 1965 in the three regions that had poorly determined epicenters and/or magnitudes, including eight events with no previously determined magnitude values. Most intensity centers for earthquakes with poorly known epicenters lay within their estimated epicentral error ellipses. For historic earthquakes with known instrumental magnitudes, magnitude estimated from intensity differed by an average of 0.5 (south-central), 1.0 (interior), and 0.05 (southeast) magnitude units. These results indicate that although intensity data in Alaska are sparse, they can be used to estimate earthquake locations and magnitudes. As additional intensity data become available, the three broad regions of Alaska can be further subdivided to reflect areas of similar geology and stress orientation and new attenuation relationships can be developed. I also anticipate that additional intensity data will allow the development of site-specific corrections to further improve epicentral and magnitude estimates from MMI data.

Attenuation relation of Arias intensity for Zagros Mountains region (Iran)

Abstract Arias intensity is considered as a shaking parameter suitable for characterizing earthquake impact on ground stability. Within the framework of a study aimed at providing tools for the assessment of hazards related to earthquake-induced slope failures, Arias intensity attenuation relations were determined for the Zagros Mountains region, an active tectonic belt elongated NW–SE in the western and south-western part of Iran. The calculation of relation coefficients was based on strong-motion data of earthquakes located in the Zagros area and recorded by Iranian stations managed by the Building and Housing Research Center of Iran (BHRC). Five models of attenuation relation were considered and their coefficients were estimated through a least-square regression analysis. The relations obtained were then applied to a data sample different from that used for regression and the root mean square (RMS) of residuals was examined in order to compare effectiveness of different relations in probabilistic estimates. Furthermore a comparison made with attenuation relations obtained for Alborz and the central part of Iran showed significant differences possibly related to structural differences.

Ground‐motion attenuation relationship for the Sumatran megathrust earthquakes

AbstractA representative attenuation relationship is one of the key components required in seismic hazard assessment of a region of interest. Attenuation relationships for peak ground acceleration, peak ground velocity and response spectral accelerations for Sumatran megathrust earthquakes, covering Mw up to 9.0, are derived based on synthetic seismograms obtained from a finite‐fault kinematic model. The relationships derived are for very hard rock site condition and for a long‐distance range between 200 and 1500 km. They are then validated with recorded data from giant earthquakes on the Sumatran megathrust occurring since year 2000. A close examination of the recorded data also shows that spectral shapes predicted by most of the existing attenuation relationships and that specified in the IBC code are not particularly suitable for sites where potential seismic hazard is dominated by large‐magnitude, distant, earthquakes. Ground motions at a remote site are typically signified by the dominance of long‐period components with periods longer than 1 s, whereas the predominant periods from most of the existing attenuation relationships and the IBC code are shorter than 0.6 s. The shifting of response spectrum towards longer period range for distant earthquakes should be carefully taken into account in the formulation of future seismic codes for Southeast Asia, where many metropolises are located far from active seismic sources. The attenuation relationship derived in the present study can properly reproduce the spectral shape from distant subduction earthquakes, and could hopefully give insights into the formulation of future seismic codes. Copyright © 2009 John Wiley & Sons, Ltd.

Real-time Performance of the Virtual Seismologist Earthquake Early Warning Algorithm in Southern California

The Virtual Seismologist (VS) method is a Bayesian approach to regional network-based earthquake early warning (EEW) that estimates earthquake magnitude, location, and the distribution of peak ground motion using observed ground motion amplitudes, predefined prior information, and appropriate attenuation relationships (Cua 2005; Cua and Heaton 2007). The application of Bayes's theorem in earthquake early warning (Cua 2005) states that the most probable source estimate at any given time is a combination of contributions from prior information (possibilities include network topology or station health status, regional hazard maps, earthquake forecasts, the Gutenberg-Richter magnitude-frequency relationship) and a likelihood function, which takes into account observations from the ongoing earthquake. Prior information can be considered relatively static over the timescale of a given earthquake rupture. The changes in the source estimates and predicted peak ground motion distribution, which are updated each second, are due to changes in the likelihood function as additional arrival and amplitude data become available. The potential use of prior information differentiates the VS approach from other regional, network-based EEW algorithms, such as ElarmS (Allen and Kanamori 2003).

Testing ElarmS in Japan

Earthquake early warning systems use seismic networks, rapid telemetry, and software algorithms to detect an earthquake immediately after its inception, estimate its damage potential, and disseminate a warning to surrounding communities before peak ground shaking occurs. Earthquake Alarm Systems, or ElarmS, is an earthquake early warning system developed in California. The ElarmS algorithm recognizes earthquakes from the initial P -wave arrivals at seismometers near the epicenter. The characteristics of the P wave, including amplitude and frequency, are used to estimate a final magnitude for the event. P -wave arrival times from several stations are combined to estimate the hypocenter of the event. Finally, the estimated magnitude and hypocenter are applied to attenuation relations to produce a prediction of ground shaking levels in the region. ElarmS has been tested extensively with datasets of earthquakes from northern and southern California (Allen and Kanamori 2003; Allen 2007; Wurman et al. 2007; Tsang et al. 2007; Allen et al. 2009). While the test datasets from California included a large range of locations and source types, there are a limited number of recent, well-recorded, large earthquakes available for testing the early warning system. In this study we take ElarmS to another geographic and seismic setting and test the algorithms with a dataset of 84 large-magnitude earthquakes, including 43 of magnitude 6.0 or greater, in Japan. The Japanese test dataset is valuable both for the insight into ElarmS' processing of large events and for the chance to process events in a completely different geologic setting. The offshore and deep nature of many of the events presents new challenges to the methodology. The Japanese earthquakes offer an opportunity to improve the robustness of ElarmS, extend its abilities to other settings, and confirm its relevance for large-magnitude events. The dataset contains 84 earthquakes recorded …

Field monitoring on the train-induced vibration response of track structure in the Beiluhe permafrost region along Qinghai–Tibet railway in China

Abstract Analyses of characteristics of vibration response of track structure from train traffic and its attenuation laws, based on the field monitoring of the vibration acceleration response of rail, sleeper, and embankment at the Beiluhe permafrost testing section along the Qinghai–Tibet railway in China, are performed in this paper. The reasonable fitting formula of attenuation relationship of embankment vibration is put forward in a negative exponential function form. The quantitative understanding of the vibration property is obtained according to the statistic of the two well-defined eigenvalues of vibration acceleration response, as well as the analysis of the acceleration time histories and the corresponding frequency spectra. The results suggest that: the effect of rail gap on the maximal vertical vibration response of rail is not evident; vibration response of sleeper near the rail gap is obviously larger than that of other sleepers, especially having intensive shock pulse, and the maximum is more than three times that of the vibration response of the sleeper lying in the very middle of the two rail gaps from one compartment passing by; the rail vibration energy concentrates within 10 Hz, and the rail predominant frequencies mainly correlate with train speed and bogie spacing; the dominant frequencies of the embankment vibration, varying from 40 to 70 Hz for the embankment shoulder and reducing with the distance increasing from the track, are influenced chiefly by train speed and sleeper spacing. The results mentioned above have important significance for rational cognition of vibration response characteristics of track structure at permafrost site, and moreover for the dynamic stability evaluation for the long-term operation of the Qinghai–Tibet railway. Meanwhile, the investigation provides basic data for the further research on the rail transit dynamics and the improvement of railroading criterion in cold regions.

Probabilistic seismic hazard map of NW Himalaya and its adjoining area, India

The seismically active Northwest (NW) Himalaya falls within Seismic Zone IV and V of the hazard zonation map of India. The region has suffered several moderate (~25), large-to-great earthquakes (~4) since Assam earthquake of 1897. In view of the major advancement made in understanding the seismicity and seismotectonics of this region during the last two decades, an updated probabilistic seismic hazard map of NW Himalaya and its adjoining areas covering 28–34°N and 74–82°E is prepared. The northwest Himalaya and its adjoining area is divided into nineteen different seismogenic source zones; and two different region-specific attenuation relationships have been used for seismic hazard assessment. The peak ground acceleration (PGA) estimated for 10% probability of exceedance in 50 and 10 years at locations defined in the grid of 0.25 × 0.25°. The computed seismic hazard map reveals longitudinal variation in hazard level along the NW Himalayan arc. The high hazard potential zones are centred around Kashmir region (0.70 g/0.35 g), Kangra region (0.50 g/0.020 g), Kaurik-Spitti region (0.45 g/0.20 g), Garhwal region (0.50 g/0.20 g) and Darchula region (0.50 g/0.20 g) with intervening low hazard area of the order of 0.25 g/0.02 g for 10% probability in 50 and 10 years in each region respectively.

Attenuation of P- and S-waves in the Chamoli Region, Himalaya, India

The attenuation properties of the crust in the Chamoli region of Himalaya have been examined by estimating the frequency-dependent relationships of quality factors for P waves (Qα) and for S waves (Qβ) in the frequency range 1.5–24 Hz. The extended coda normalization method has been applied on the waveforms of 25 aftershocks of the 1999 Chamoli earthquake (M 6.4) recorded at five stations. The average value of Qα is found to be varied from 68 at 1.5 Hz to 588 at 24 Hz while it varies from 126 at 1.5 Hz to 868 at 24 Hz for Qβ. The estimated frequency-dependent relations for quality factors are Qα = (44 ± 1)f(0.82±.04) and Qβ = (87 ± 3)f(0.71±.03). The rate of increase of Q(f) for P and S waves in the Chamoli region is comparable with the other regions of the world. The ratio Qβ/Qα is greater than one in the region which along with the frequency dependence of quality factors indicates that scattering is an important factor contributing to the attenuation of body waves in the region. A comparison of attenuation relation for S wave estimated here (Qβ = 87f0.71) with that of coda waves (Qc = 30f1.21) obtained by Mandalet al. (2001) for the same region shows that Qc > Qβ for higher frequencies (>8 Hz) in the region. This indicates a possible high frequency coda enrichment which suggests that the scattering attenuation significantly influences the attenuation of S waves at frequencies >8 Hz. This observation may be further investigated using multiple scattering models. The attenuation relations for quality factors obtained here may be used for the estimation of source parameters and near-source simulation of earthquake ground motion of the earthquakes, which in turn are required for the assessment of seismic hazard in the region.

Practical Site-Specific Earthquake Early Warning Application

Real-time hazard mitigation we have developed using earthquake early warning (EEW) (1) enhances seismic intensity estimation accuracy and (2) extends the interval between when an EEW is issued and when strong tremors arrive. We accomplished the first point (enhancing seismic intensity estimation) by reducing estimation error to less than that commonly used based on an attenuation relationship and soil amplification factor by considering source-location and wave propagation path differences based on site-specific empiricism. We accomplished the second point (shortening the time between warnings and when tremors arrive) using a high-speed, reliable communication network for receiving EEW information from the Japan Meteorological Agency (JMA) and quickly transmitting warning signals to users. In areas close to quake epicenters, however, warnings may not arrive before the arrival of strong ground motions. The on-site warning system we developed uses P-wave pickup sensors that detect P-wave arrival at a site and predict seismic intensity of subsequent S-waves. We confirmed the on-site warning prototype’s feasibility based on numerical simulation and observation. We also developed an integration server for combining on-site warnings with JMA information to be applied to earthquakes over a wide range of distances. We installed a practical prototype at a construction site near the 2008 Iwate-Miyagi Inland Earthquake epicenter to measure its aftershocks because JMA EEW information was too late to use against the main shock. We obtained good aftershock results, confirming the prototype’s applicability and accuracy. Integration server combination logic was developed for manufacturing sites requiring highly robust, reliable control.