Finite-fault Model Research Articles

The 25 October 2010 Mentawai tsunami earthquake, from real-time discriminants, finite-fault rupture, and tsunami excitation

[1] The moment magnitude 7.8 earthquake that struck offshore the Mentawai islands in western Indonesia on 25 October 2010 created a locally large tsunami that caused more than 400 human causalities. We identify this earthquake as a rare slow-source tsunami earthquake based on: 1) disproportionately large tsunami waves; 2) excessive rupture duration near 125 s; 3) predominantly shallow, near-trench slip determined through finite-fault modeling; and 4) deficiencies in energy-to-moment and energy-to-duration-cubed ratios, the latter in near-real time. We detail the real-time solutions that identified the slow-nature of this event, and evaluate how regional reductions in crustal rigidity along the shallow trench as determined by reduced rupture velocity contributed to increased slip, causing the 5–9 m local tsunami runup and observed transoceanic wave heights observed 1600 km to the southeast.

Enhancement of long period components of recorded and synthetic ground motions using InSAR

Tall buildings and flexible structures require a better characterization of long period ground motion spectra than the one provided by current seismic building codes. Motivated by that, a methodology is proposed and tested to improve recorded and synthetic ground motions which are consistent with the observed co-seismic displacement field obtained from interferometric synthetic aperture radar (InSAR) analysis of image data for the Tocopilla 2007 earthquake ( M w =7.7) in Northern Chile. A methodology is proposed to correct the observed motions such that, after double integration, they are coherent with the local value of the residual displacement. Synthetic records are generated by using a stochastic finite-fault model coupled with a long period pulse to capture the long period fling effect. It is observed that the proposed co-seismic correction yields records with more accurate long-period spectral components as compared with regular correction schemes such as acausal filtering. These signals provide an estimate for the velocity and displacement spectra, which are essential for tall-building design. Furthermore, hints are provided as to the shape of long-period spectra for seismic zones prone to large co-seismic displacements such as the Nazca-South American zone.

Improvements of corner frequency and scaling factor for stochastic finite-fault modeling

In this paper, three existing source spectral models for stochastic finite-fault modeling of ground motion were reviewed. These three models were used to calculate the far-field received energy at a site from a vertical fault and the mean spectral ratio over 15 stations of the Northridge earthquake, and then compared. From the comparison, a necessary measure was observed to maintain the far-field received energy independent of subfault size and avoid overestimation of the long-period spectral level. Two improvements were made to one of the three models (i.e., the model based on dynamic corner frequency) as follows: (i) a new method to compute the subfault corner frequency was proposed, where the subfault corner frequency is determined based on a basic value calculated from the total seismic moment of the entire fault and an increment depending on the seismic moment assigned to the subfault; and (ii) the difference of the radiation energy from each subfault was considered into the scaling factor. The improved model was also compared with the unimproved model through the far-field received energy and the mean spectral ratio. The comparison proves that the improved model allows the received energy to be more independent of subfault size than the unimproved model, and decreases the overestimation degree of the long-period spectral amplitude.

Stochastic Strong Ground Motion Simulation of the 12 November 1999 Duzce (Turkey) Earthquake Using a Dynamic Corner Frequency Approach

On 12 November 1999, only three months after the 17 August 1999 Kocaeli earthquake (Mw 7:4), an earthquake of Mw 7:1 occurred immediately to the east of the Kocaeli rupture in northwestern Turkey resulting in extensive structural damage in the city of Duzce and its surrounding area. It was reported to be a right- lateral strike slip event on the previously unbroken segment of the North Anatolian fault zone with a north-dipping fault plane. This paper presents stochastic finite-fault simulation of near-field ground motions from this earthquake at selected near-fault stations based on a dynamic corner frequency approach using the computer program EXSIM (Motazedian and Atkinson, 2005). The method requires region-specific source, path, and site characterizations as input model parameters. The source mech- anism of the 1999 Duzce event and regional path effects are well constrained from previous studies of the earthquake. The local site effects at the selected stations are studied as a combination of the kappa operator and frequency-dependent soil ampli- fication. The model parameters are validated against recordings and a stress-drop value of 100 bars is estimated for the 1999 Duzce earthquake. The validated model is then used to compute synthetic records around the fault. Distribution of peak ground-motion parameters is observed to be consistent with the building damage dis- tribution in the near-fault region most affected by the seismic shaking. The attenuation of synthetic ground-motion parameters is compared with recent ground-motion pre- diction equations proposed for the region by Gulkan and Kalkan (2002), Ulusay et al. (2004), and Akkar and Bommer (2007), as well as two next generation attenuation models by Boore and Atkinson (2007) and Campbell and Bozorgnia (2007). Despite discrepancies at several stations, stochastic finite-fault modeling based on a dynamic corner frequency approach confirms to be a practical tool to reproduce the ground motions of large earthquakes.

Estimation of Strong Ground Motions for 2001 Bhuj (M w 7.6), India Earthquake

The strong ground motions for the 2001 Bhuj (Mw 7.6) India earthquake have been estimated on hard rock and B/C boundary (NEHRP) levels using a recently modified version of stochastic finite fault modeling based on dynamic corner frequency (Motazedian and Atkinson in Bull Seismol Soc Am 95, 995–1010 2005). Incorporation of dynamic corner frequency removes the limitations of earlier stochastic methods. Simulations were carried out at 13 sites in Gujarat where structural response recorder (SRR) recordings are available. In addition, accelerograms were simulated at the B/C boundary at a large number of points distributed on a grid. The corresponding response spectra have also been estimated. The values of peak ground accelerations and spectral accelerations at three periods (0.4, 0.75 and 1.25 s) are presented in the form of contour maps. The maximum value of peak ground acceleration (PGA) in the center of meizoseismal zone is 550 cm/s2. The response spectral acceleration in same zone is 900 cm/s2 (T = 0.4 s), 600 cm/s2 (T = 0.75 s) and 300 cm/s2 (T = 1.25 s). The innermost PGA contour is on the fault plane. A comparison of the PGA values obtained at 13 sites in this study with those obtained in earlier studies on the same sites, but employing different methods, show that the present PGA values are comparable at most of the sites. The rate of decay of PGA values is fast at short distances as compared to that at longer distances. The PGA values obtained here put some constraints on the expected values from a similar earthquake in the region. A synthetic intensity map has been prepared from the estimated values of PGA using an empirical relation. A comparison with the reported intensity map of the earthquake shows the synthetic MMI values, as expected, are lower by 1 unit compared to reported intensity map. The contour map of PGA along with the contour maps of spectral acceleration at various periods permit the assessment of damage potential to various categories of houses and other structures. Such information will be quite important in planning of mitigation and disaster management programs in the region.

Hybrid slip model for near-field ground motion estimation based on uncertainty of source parameters

The hybrid slip model used to generate a finite fault model for near-field ground motion estimation and seismic hazard assessment was improved to express the uncertainty of the source form of a future earthquake. In this process, source parameters were treated as normal random variables, and the Fortran code of hybrid slip model was modified by adding a random number generator so that the code could generate many finite fault models with different dimensions and slip distributions for a given magnitude. Furthermore, a simple method to choose an optimal one from these generated models was proposed. The 1994 Northridge earthquake was taken as an example to demonstrate the procedure of the application of the improved model. Three rock stations, LV3, MCN and PCD, in near-field were used to compare the simulated ground motion from the improved model and optimal model with the observed one. The agreement between them in the periods of interest indicates that the improved model and the method to choose the optimal model are available for the engineering practice of ground motion estimation.

A Method to Establish Seismic Noise Baselines for Automated Station Assessment

Currently, the United States Geological Survey (USGS) National Earthquake Information Center (NEIC) receives more than 4,000 channels of seismic data from roughly 900 seismic stations distributed around the world in near real time. As the NEIC develops increasingly sophisticated methods for automated data processing, it becomes equally important to develop tools for ensuring that only the highest-quality data are used in rapid earthquake products. In this paper, we present methods and applications for computing long- and short-term, station-specific noise baselines for broadband seismic data channels. Long-term baselines (one year or greater) are useful for determining ambient noise conditions, while short-term baselines (one hour to one month) are useful for monitoring changing station performance and noise characteristics. This method is currently in testing and development at the NEIC for evaluation of instrument responses, assessment of data quality for real-time earthquake processing systems, new station site evaluation, and assessment of gross network characteristics. Real-time earthquake processing systems at the NEIC rely on high-quality seismic data to compute accurate earthquake locations and magnitudes, moment-tensor solutions, finite-fault models, and shaking intensity. The NEIC receives real-time seismic data from a variety of contributors including: global networks (Global Seismographic Network [GSN], GEOSCOPE, GEOFON), national networks (ANSS, Australia, Spain, Canada, Switzerland), regional networks (ANZA, PRSN, CISN, PNWSN, AEIC), government agencies (National Oceanic and Atmospheric Administration [NOAA] tsunami warning centers, the International Monitoring System [IMS]), and temporary deployments such as the EarthScope transportable array (TA). On most days, approximately 10% of contributed instrument responses are either not known or are erroneous and cannot be used for accurate real-time amplitude information. Maintaining accurate and current metadata for roughly 900 contributed stations is difficult when instrumentation upgrades or other changes occur regularly. Automated processing of real-time seismic data necessitates the development of automated tools and procedures to quickly identify changes …

Coseismic stress parameter of three California Earthquakes derived from the stochastic finite fault technique

Stochastic finite fault modeling is used to derive the coseismic stress parameter distribution on the fault surface of three well-recorded California earthquakes: M7.0, 1989, Loma Prieta; M7.3, 1992, Landers; and M6.7, 1994, Northridge. Classical waveform inversion techniques are inherently more powerful than stochastic modeling as a means of deriving detailed source parameters. However, the application of stochastic methods to the source modeling problem is useful to: (1) explore and calibrate the limitations and boundaries of stochastic modeling, (2) understand its relationship to more deterministically based techniques, and (3) provide a view of the source radiation not available from deterministic modeling. The stress parameter distribution for the M7.0 1989 Loma Prieta earthquake fault shows a concentration of stress in the lower part of the northwest side of the fault and another concentration in the upper southeast side of the fault, with an average stress parameter of 80 bars over the fault surface. The stress parameter distribution for the M7.3 1992 Landers earthquake fault shows a gradual increase of stress starting from the southeast side of the fault, close to the hypocenter, towards the center. The maximum stress occurs in the lower central part of the modeled fault surface. The average stress parameter is 70 bars for the Landers earthquake. The stress parameter distribution of the M6.7 1994 Northridge earthquake shows a concentration at the lower southeast end of the fault surface, extending toward the center of the fault surface and stretching to the northwest end. The average stress parameter is 80 bars for Northridge earthquake. The stress parameter distributions derived in this study by stochastic finite-fault modeling of high-frequency motions show considerable similarity to many of the slip distributions provided by different research groups for the same earthquakes, suggesting that the derivation of stress parameter distribution on a fault surface by the method applied in this study is reliable and closely tied to slip on the fault.

Dynamic corner frequency in source spectral model for stochastic synthesis of ground motion

The static corner frequency and dynamic corner frequency in stochastic synthesis of ground motion from finite-fault modeling are introduced, and conceptual disadvantages of the two are discussed in this paper. Furthermore, the non-uniform radiation of seismic wave on the fault plane, as well as the trend of the larger rupture area, the lower corner frequency, can be described by the source spectral model developed by the authors. A new dynamic corner frequency can be developed directly from the model. The dependence of ground motion on the size of subfault can be eliminated if this source spectral model is adopted in the synthesis. Finally, the approach presented is validated from the comparison between the synthesized and observed ground motions at six rock stations during the Northridge earthquake in 1994.

Predicted Ground Motions for Great Interface Earthquakes in the Cascadia Subduction Zone

Ground motions for earthquakes of moment magnitude ( M ) 7.5–9.0 on the Cascadia subduction zone interface are simulated based on a stochastic finite-fault model and used to estimate average response spectra for firm-site conditions in Vancouver, Victoria, and Seattle. We also express the response spectra as ground-motion prediction equations (GMPEs) for Cascadia events. The simulations are calibrated by modeling the wealth of ground-motion data from the M 8.1 Tokachi-Oki earthquake sequence of Japan. Adjustments to the calibrated model are made to consider average source, attenuation, and site parameters for the Cascadia region. We perform best estimate simulations for a preferred set of input parameters. Typical results suggest mean values of 5%-damped pseudoacceleration in the range from about 100 to 200 cm/sec2, at frequencies from 1 to 4 Hz, for firm-ground conditions in Vancouver, Victoria, and Seattle. Uncertainty in stress drop causes uncertainty in simulated response spectra of about ±50%. Uncertainties in the attenuation model produce even larger uncertainties in response spectral amplitudes—a factor of about 2 at 100 km, becoming even larger at greater distances. It is thus important to establish the regional attenuation model for ground-motion simulations. Furthermore, combining data from regions with different attenuation characteristics—in particular Japan and Mexico—into a global subduction zone database for development of global empirical GMPEs may not be a sound practice. Time histories of acceleration for the stochastically simulated motions are provided for reference sites in Vancouver, Victoria, and Seattle. An alternative set of motions, based on lightly modifying real recordings from the Tokachi-Oki earthquake to match expected conditions for Cascadia cities, are also provided. These alternative records have similar spectral content to the simulated motions but contain additional complexity and more realistic phasing. The provision of alternative record sets allows users to conduct studies to determine the importance of these effects for structural response.

Predicting Probabilistic-Based Strong Ground Motion Time Series for Citadel of Arg-E-Bam (South-East of Iran)

The main objective of this article is to present a probabilistic-based strong motion compatible with the source-path and site soil condition given the probability of exceedence for citadel of Arg-e-Bam site bed rock (South-East of Iran). A Fourier amplitude spectral attenuation relation for bed rock beneath the site is proposed which permits the estimation of time-histories through a probabilistic seismic hazard analysis procedure. Due to lack of data, the two well-known simulation techniques, point source and finite fault models have been used for generating hundreds of strong motion as input data. Tens of model parameter values such as stress-drop nucleation points were used, in each specified magnitude-distance, to reduce the uncertainty effects inherently existing in seismological/geological parameters. The proposed attenuation relation is validated by comparing the estimated strong motion, in the form of Fourier amplitude spectral, using the proposed attenuation relation with those of recorded ground motion data at three stations far away from the assumed source so that the results would not be influenced by the near source problems such as directivity and fling step. The results of proposed technique is assessed by comparing the estimated response spectra, with 10% probability of exceedence and 5% damping ratio, with those of traditional uniform hazard spectra. The proposed technique is supposed to be used in retrofitting procedure of international historical adobe structures in Arg-e-Bam site, which have been damaged during the destructive Bam earthquake 2003, Iran

Deterministic Seismic Scenarios for Imphal City

In this article, the spatial variation of ground motion in Imphal City has been estimated by the finite-fault seismological model coupled with site response analysis. The important seismic sources around Imphal City have been identified from the fault map and past seismicity data. The rock level acceleration time histories at Imphal City for the 1869 Cachar (Mw 7.5) earthquake and a hypothetical Mw 8.1 event in the Indo-Burma subduction zone have been estimated by a stochastic finite-fault model. Soil investigation data of 122 boreholes have been collected from several construction projects in Imphal City. Site response analysis has been carried out and the surface level ground motion has been determined for Imphal City for these two earthquake events. The results are presented in the form of peak ground acceleration (PGA) contour map. From the present study it has been ascertained that the maximum amplification for PGA over Imphal City is as high as 2.5. The obtained contour maps can serve as guidelines for identifying vulnerable areas and disaster mitigation in Imphal City.

Rapid Estimation of Source Parameters Using Finite Fault Modeling--Case Studies from the Sikkim and Garhwal Himalayas

Research Article| January 01, 2009 Rapid Estimation of Source Parameters Using Finite Fault Modeling—Case Studies from the Sikkim and Garhwal Himalayas A. Raj; A. Raj Indian Institute of Technology Kharagpur 721302 West Bengal, India nath@gg.iitkgp.ernet.in (S. K. N.) 1Indian Institute of Technology, Kharagpur Search for other works by this author on: GSW Google Scholar S. K. Nath; S. K. Nath Indian Institute of Technology Kharagpur 721302 West Bengal, India nath@gg.iitkgp.ernet.in (S. K. N.) 1Indian Institute of Technology, Kharagpur Search for other works by this author on: GSW Google Scholar B. K. Bansal; B. K. Bansal Indian Institute of Technology Kharagpur 721302 West Bengal, India nath@gg.iitkgp.ernet.in (S. K. N.) 2Seismology Division, Ministry of Earth Sciences, India Search for other works by this author on: GSW Google Scholar K. K. S. Thingbaijam; K. K. S. Thingbaijam Indian Institute of Technology Kharagpur 721302 West Bengal, India nath@gg.iitkgp.ernet.in (S. K. N.) 1Indian Institute of Technology, Kharagpur Search for other works by this author on: GSW Google Scholar A. Kumar; A. Kumar Indian Institute of Technology Kharagpur 721302 West Bengal, India nath@gg.iitkgp.ernet.in (S. K. N.) 3Indian Institute of Technology, Roorkee Search for other works by this author on: GSW Google Scholar N. Thiruvengadam; N. Thiruvengadam Indian Institute of Technology Kharagpur 721302 West Bengal, India nath@gg.iitkgp.ernet.in (S. K. N.) 1Indian Institute of Technology, Kharagpur Search for other works by this author on: GSW Google Scholar A. Yadav; A. Yadav Indian Institute of Technology Kharagpur 721302 West Bengal, India nath@gg.iitkgp.ernet.in (S. K. N.) 1Indian Institute of Technology, Kharagpur Search for other works by this author on: GSW Google Scholar M. L. Arrawatia M. L. Arrawatia Indian Institute of Technology Kharagpur 721302 West Bengal, India nath@gg.iitkgp.ernet.in (S. K. N.) 4Department of Science and Technology, Sikkim Search for other works by this author on: GSW Google Scholar Author and Article Information A. Raj 1Indian Institute of Technology, Kharagpur Indian Institute of Technology Kharagpur 721302 West Bengal, India nath@gg.iitkgp.ernet.in (S. K. N.) S. K. Nath 1Indian Institute of Technology, Kharagpur Indian Institute of Technology Kharagpur 721302 West Bengal, India nath@gg.iitkgp.ernet.in (S. K. N.) B. K. Bansal 2Seismology Division, Ministry of Earth Sciences, India Indian Institute of Technology Kharagpur 721302 West Bengal, India nath@gg.iitkgp.ernet.in (S. K. N.) K. K. S. Thingbaijam 1Indian Institute of Technology, Kharagpur Indian Institute of Technology Kharagpur 721302 West Bengal, India nath@gg.iitkgp.ernet.in (S. K. N.) A. Kumar 3Indian Institute of Technology, Roorkee Indian Institute of Technology Kharagpur 721302 West Bengal, India nath@gg.iitkgp.ernet.in (S. K. N.) N. Thiruvengadam 1Indian Institute of Technology, Kharagpur Indian Institute of Technology Kharagpur 721302 West Bengal, India nath@gg.iitkgp.ernet.in (S. K. N.) A. Yadav 1Indian Institute of Technology, Kharagpur Indian Institute of Technology Kharagpur 721302 West Bengal, India nath@gg.iitkgp.ernet.in (S. K. N.) M. L. Arrawatia 4Department of Science and Technology, Sikkim Indian Institute of Technology Kharagpur 721302 West Bengal, India nath@gg.iitkgp.ernet.in (S. K. N.) Publisher: Seismological Society of America First Online: 09 Mar 2017 Online ISSN: 1938-2057 Print ISSN: 0895-0695 © 2009 by the Seismological Society of America Seismological Research Letters (2009) 80 (1): 89–96. https://doi.org/10.1785/gssrl.80.1.89 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 A. Raj, S. K. Nath, B. K. Bansal, K. K. S. Thingbaijam, A. Kumar, N. Thiruvengadam, A. Yadav, M. L. Arrawatia; Rapid Estimation of Source Parameters Using Finite Fault Modeling—Case Studies from the Sikkim and Garhwal Himalayas. Seismological Research Letters 2009;; 80 (1): 89–96. doi: https://doi.org/10.1785/gssrl.80.1.89 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySeismological Research Letters Search Advanced Search Earthquake source parameters provide information about the source properties of individual shocks, which can serve as an important basis for generalization about, and synthesis of, strong ground motion. Source function is also one of the most important contributors to seismic hazard analysis because it provides information about the seismic energy released during an earthquake. Recent advances in seismic source theory have improved our understanding of body wave spectral characteristics and physical properties of the source such as seismic moment, stress drop, and the area of rupture. Brune (1970) developed a model to calculate source parameters using near and... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Spatio-temporal rupture process of the 2008 great Wenchuan earthquake

Focal mechanism and dynamic rupture process of the Wenchaun M s8.0 earthquake in Sichuan province on 12 May 2008 were obtained by inverting long period seismic data from the Global Seismic Network (GSN), and characteristics of the co-seismic displacement field near the fault were quantitatively ana-lyzed based on the inverted results to investigate the mechanism causing disaster. A finite fault model with given focal mechanism and vertical components of the long period P-waves from 21 stations with evenly azimuthal coverage were adopted in the inversion. From the inverted results as well as after-shock distribution, the causative fault of the great Wenchuan earthquake was confirmed to be a fault of strike 225°/dip 39°/rake 120°, indicating that the earthquake was mainly a thrust event with right-lateral strike-slip component. The released scalar seismic moment was estimated to be about 9.4×1020―2.0×1021 Nm, yielding moment magnitude of M w7.9―8.1. The great Wenchuan earthquake occurred on a fault more than 300 km long, and had a complicated rupture process of about 90 s duration time. The slip distribution was highly inhomogeneous with the average slip of about 2.4 m. Four slip-patches broke the ground surface. Two of them were underneath the regions of Wenchuan-Yingxiu and Beichuan, respectively, with the first being around the hypocenter (rupture initiation point), where the largest slip was about 7.3 m, and the second being underneath Beichuan and extending to Pingwu, where the largest slip was about 5.6 m. The other two slip-patches had smaller sizes, one having the maximum slip of 1.8 m and lying underneath the north of Kangding, and the other having the maximum slip of 0.7 m and lying underneath the northeast of Qingchuan. Average and maximum stress drops over the whole fault plane were estimated to be 18 MPa and 53 MPa, respectively. In addition, the co-seismic displacement field near the fault was analyzed. The results indicate that the features of the co-seismic displacement field were coincident with those of the intensity distribution in the meizo-seismal area, implying that the large-scale, large-amplitude and surface-broken thrust dislocation should be responsible for the serious disaster in the near fault area.

Real-time seismology for the 05/12/2008 Wenchuan earthquake of China: A retrospective view

The devastating 05/12/2008 Wenchuan earthquake (Mw7.9) in Sichuan Province of China showed very few precursory phenomena and occurred on a fault system once assigned to be of moderate long term seismic risk. Given the existing coverage of seismograph stations in Sichuan Province, real-time seismology could have been effective in avoiding some earthquake damage and helping post-earthquake emergency response. In a retrospective view, we demonstrated that the epicenter can be located with 20 km accuracy using just two broadband stations with three-component, which takes only about 10 s after the onset of the earthquake. Initial magnitude is estimated to be M7 with the Tc measurement over first 4 seconds of P waves. Better magnitude estimate can be obtained within 2 min by modeling Pnl waves for stations about 500 km away where the S waveforms are clipped. The rupture area is well revealed by teleseismically-recorded >M5 early aftershocks within two hours after the mainshock. Within a few hours, teleseismic body waves were inverted to derive a more detailed rupture process and the finite fault model can be readily used to calculate ground motions, thus providing vital information for rescue efforts in the case where no real-time strong motion records are available.

Soil-Column Depth-Dependent Seismic Site Coefficients and Hazard Maps for the Upper Mississippi Embayment

Abstract The presence of deep unconsolidated deposits in the Upper Mississippi Embayment (UME) has an important impact on surface motions and has been the subject of several studies including a study by two of us, who integrated probabilistic seismic hazard analysis (PSHA) with nonlinear site effects (NL). This study extends the PSHA–NL procedure to (1) incorporate a finite-fault model capable of generating near-source motions instead of using point-source models only, (2) better approximate the range of available attenuation relations for the Central and Eastern United States (CEUS), (3) examine the hazard at very high levels of shaking, and (4) propagate generated rock motions through randomized soil profile properties to achieve a more consistent probabilistic procedure. The extended PSHA–NL procedure is used to develop updated depth-dependent site coefficients for the UME, which generally provides a lower hazard at short periods but a higher hazard at longer periods than current approaches. Proposed probabilistic seismic hazard maps, at selected spectral accelerations, that incorporate the proposed site effects are also presented for the UME and are systematically compared with seismic hazard maps proposed by others.

Erratum to Kinematic Inversion of the 2004 M 6.0 Parkfield Earthquake Including an Approximation to Site Effects

It has been brought to our attention by users of the kinematic finite-fault models published for the 2004 Parkfield earthquake in Liu et al. (2006) that the values in Table 2 (p. S149) are not correct. In fact, we erroneously published preliminary values …

Erratum to Stochastic Finite-Fault Modeling of Strong Ground Motions from the 26 December 2003 Bam, Iran, Earthquake

Equation (6) of Shoja-Taheri and Ghofrani (2007) was inadvertently deleted from page 1956. BSSA regrets the error. The equation is included here, along with surrounding text. Corrected text: To compare the attenuation of the synthetic ground motions with the attenuation relation for the region (Shoja-Taheri et al., 2005), we simulated accelerograms for nearly 5000 nodes in a mesh covering the area shaken by this earthquake. We assumed that all the stations in the area are located on rock. We fitted the simulated PGAs using

Probabilistic seismic hazard analysis at selected sites in Addis Ababa, Ethiopia

This study presents probabilistic seismic hazard analysis at three specific sites namely: Bole area (south), Nani Building site (middle) and Gulele area (north) that represent the most often encountered subsurface profiles in Addis Ababa (AA), capital city of Ethiopia. The methodology followed couples conventional PSHA with non-linear dynamic analyses of the soil column subjected to synthetic ground motions. A fully probabilistic method was used that incorporates all major uncertainties which substantially affect the hazard levels of ground motion. Reference (stiff site) seismic hazard was determined using finite fault model in which input parameters treated randomly as discussed in our companion article. The hazard at the soil surface was computed by convolving the site-specific hazard curve at stiff site with the probability distribution of the amplification function. Within period range less than 0.50 second, a statistical treatment between surface spectral acceleration, (<i>S_a^s</i>) and that of the stiff site, ((<i>S_a^s(T)</i>) fitted to quadratic model of amplification function, <i>AF(T)</i> at the same period, <i>T</i> demonstrated a reasonable correlation. The Surface hazard was estimated using the developed relation for the specified period range. Closer to the fundamental periods of the soil columns, a strong correlation was manifested at the three selected sites.

Estimation of Nonlinear Soil Behavior During the 1999 Chi-Chi, Taiwan, Earthquake

The 1999 Chi-Chi, Taiwan, earthquake (Mw = 7.6) was one of the strongest earthquakes in recent years recorded by a large number of strong-motion devices. Though only surface records are available, the obtained strong-motion database indicates the variety of ground responses in the near-fault zones. In this study, accelerograms of the Chi-Chi earthquake were simulated at rock and soil sites, and models of soil behavior were constructed at seven soil sites (TCU065, TCU072, TCU138, CHY026, CHY104, CHY074, and CHY015), for which parameters of the soil profiles are known down to depths of at least ~70 m and at 24 other soil sites, for which parameters of the soil profiles are known down to 30–40 m; all the sites were located within ~50 km from the fault. For reconstructing stresses and strains in the soil layers, we used a method similar to that developed for the estimation of soil behavior based on vertical array records. As input for the soil layers, acceleration time histories simulated by stochastic finite-fault modelling with a prescribed slip distribution over the fault plane were taken. In spite of the largeness of the earthquake’s magnitude and the proximity of the studied soil sites to the fault plane, the soil behavior at these sites was relatively simple, i.e., a fairly good agreement between the spectra of the observed and simulated accelerograms and between their waveforms was obtained even in cases where a single stress-strain relation was used to describe the behavior of whole soil thickness down to ~70–80 m during strong motion. Obviously, this is due to homogeneity in the characteristics of soil layers in depth. At all the studied sites, resonant phenomena in soil layers (down to ~40–60 m) and nonlinearity of soil response were the main factors defining soil behavior. At TCU065, TCU110, TCU115, CHY101, CHY036, and CHY039 liquefaction phenomena occurred in the upper soil layers, estimated strains achieved ~0.6–0.8%; at other stations, maximum strains in the soil layers were as high as 0.1–0.4%, according to our estimates. Thus, valuable data on the in situ soil behavior during the Chi-Chi earthquake was obtained. Similarity in the behavior of similar soils during the 1995 Kobe, 2000 Tottori (Japan), and Chi-Chi (Taiwan) earthquakes was found, indicating the possibility of forecasting soil behavior in future earthquakes. In the near-fault zones of the three earthquakes, “hard-type” soil behavior and resonant phenomena in the upper surface layers prevail, both leading to high acceleration amplitudes on the surface.