Estimation Of Seismic Risk Research Articles

Some Contributions of the Neo-Deterministic Seismic Hazard Assessment Approach to Earthquake Risk Assessment for the City of Sofia

This paper describes the outcome of the advanced seismic hazard and seismic risk estimates recently performed for the city of Sofia, based on the state-of-the-art of knowledge for this site. Some major results of the neo-deterministic, scenario-based, seismic hazard assessment approach (NDSHA) to the earthquake hazard assessment for the city of Sofia are considered. Further validations of the recently constructed synthetic strong motion database, containing site and seismic source-specific ground motion time histories are performed and discussed. Displacement and acceleration response spectra are considered. The elastic displacement response spectra and displacement demand are discussed with regard to earthquake magnitude, seismic source-to-site distance, seismic source mechanism, and local geological site conditions. The elastic response design spectrum from the standard pseudo-acceleration, versus natural period, Tn, format, converted to a capacity diagram in Sa − Sd format is discussed in the perspective of the Eurocode 8 provisions. A brief overview of the engineering applications of the seismic demand obtained making use of the NDSHA is supplied. Some applications of the outcome of NDSHA procedure for engineering purposes are shown. The obtained database of ground shaking waveforms and time-histories, computed for city of Sofia is used to: (1) extract maximum particle velocities; (2) calculate the space distribution of the horizontal strain factor Log10 e; (3) estimate liquefaction susceptibility in terms of standard penetration test, N values, and initial over burden stress; (4) estimate damage index distribution; and (5) map the distribution of the expected pipe breaks and red-tagged buildings for given scenario earthquakes, etc. The theoretically obtained database, based on the simultaneous treatment of the data from many disciplines, contains data fully suitable for practical use. The proper use of this database can lead to a significant seismic vulnerability reduction and thus contributes to earthquake preparedness.

Dislocations caused by ancient strong earthquakes in the Elbrus region

The probability of natural disastrous phenomena in the Northern Caucasus is a topical scientific problem. According to materials of the Map of General Seismic Zonation of the Russian Federation, the Elbrus region belongs to the seismic impact zone with a magnitude of as much as 8 or 9 [1]. Estimation of seismic risk for the Caucasian region based on the cluster analysis of geological–geophysical and seismological data [2] showed that the Elbrus region includes a potential seismic focus (PSF) with a predictable maximal magnitude of expected earthquakes equal to 7.2 [3]. At the same time, the region also incorporates a vast calm zone in terms of seismicity, for which any instrumental and macroseismic data on earthquakes are absent. This situation is accounted for by the fact that the melt in a vast magma chamber existing at present beneath Mt. Elbrus in the central part of the Earth’s crust [4–6] promotes the stress relief. Therefore, strong seismic quakes do Dislocations Caused by Ancient Strong Earthquakes in the Elbrus Region E. A. Rogozhin, A. N. Ovsyuchenko, and A. V. Marakhanov Presented by Academician S.A. Fedotov August 17, 2007

Source-related variations of ground motions in 3-D media: application to the Newport-Inglewood fault, Los Angeles Basin

SUMMARY Deterministic earthquake scenario simulations are playing an increasingly important role in seismic hazard and risk estimation. Our aim is to calculate a substantial number of different finite-source scenarios, embedded in a 3-D structure for a particular fault or fault system, by pre-calculating numerical Green’s functions (NGFs). A large seismic fault is divided into subfaults of appropriate size for which synthetic Green’s functions at the surface are calculated and stored. Consequently, ground motions from arbitrary kinematic sources can be simulated for the whole fault or parts of it, by superposition. To illustrate this approach and its functionalities we simulate M 7 (up to 0.5 Hz) scenario earthquakes for a simplified model of the Newport-Inglewood (NI) fault in the Los Angeles (LA) Basin. We quantify the variations of surface ground motion (e.g. peak ground velocity PGV and synthetic seismograms) due to source parameters (e.g. hypocentre location and corresponding slip history). The results show a complex behaviour, with dependence of absolute PGV and its variation on asperity location, source directionality and local structure and demonstrate the necessity to combine 3-D structural and finite-source effects to quantify ground motion characteristics and their variations.

Increased Accuracy of Vector-IM-Based Seismic Risk Assessment?

The vector-valued ground motion intensity measure (IM) consisting of spectral acceleration at two different periods is considered for seismic risk assessment of structures. The first component of the IM is the spectral acceleration at the first-mode structural period T 1. The second period is selected to increase efficiency in the estimation of seismic risk (i.e., minimizing dispersion). A method to assess vector structural fragility using a scalar global measure of structural performance is proposed. With reference to an example RC frame structure, the accuracy of prediction of the seismic risk using the considered vector IM vs. a conventional scalar IM is presented. In both cases, probabilistic seismic hazard analysis (scalar and vector) is carried out by means of a subset simulation approach that employs a stochastic model of ground motion. Results show that an effective choice of the second period T2 leads to an estimate of the seismic risk close to that obtained employing the scalar IM consisting of Sa(T1) only, while reducing the associated dispersion in the estimate. For the examined example structure, however, the reduction is negligible in light of the effort required for switching from a scalar to a vector IM.

Recent Seismic Microzoning Maps in Japan

In Japan, seismic microzoning has been conducted as the basis for better disaster planning by governments. This paper introduces various seismic microzoning maps published by the central and local governments in Japan after the 1995 Kobe earthquake. Nation-wide seismic hazard maps are published by the Headquarters for Earthquake Research Promotion, to understand the general view of seismic hazard nationwide. Regional seismic microzoning maps are prepared by the Central Disaster Prevention Council for large subduction earthquakes and the Tokyo Metropolitan earthquake. Based on results of the microzonings, strategies are proposed for disaster mitigation of the earthquakes. Local governments prepare more detailed, smaller scale maps, e.g., the Yokohama shake map using a 50 m mesh system. After the publication of the map, the numbers of applicants for seismic performance appraisal service of wooden houses and for seismic retrofitting subsidies from the city increased significantly. This stimulated central and local governments, which started detailed mapping studies. Seismic microzoning maps are being used not only for governments but also for citizens. The maps should evolve both for more attractive presentation to deepen citizens' understanding and for more reliable and comprehensive estimates of seismic hazard and risk.

Seismic hazard due to small-magnitude, shallow-source, induced earthquakes in The Netherlands

The Netherlands has large on-land gas reservoirs, which are being exploited since 1960. Small-magnitude ( M L ≤ 3.5), shallow (depth < 4 km) events induced by this gas exploitation cause light damage and much concern to the regional population. As one of the consequences the Dutch law requires since 2003 seismic hazard and risk estimates for each mining concession. Up to now only general quantitative hazard estimates, maximum possible earthquake and maximum possible intensity were available. Here we provide more specific quantitative hazard estimates. A long-term monitoring program shows a stationary rate of seismicity since 1992, probably coupled to a stationary production rate. Based on this we present a first order site-specific hazard estimate using a Probablistic Seismic Hazard Analysis (PSHA). We predict, and observe, relatively high Peak Ground Accelerations (PGA). PGA above 0.2 g is not unusual, but damage has so far been restricted to non-structural damage, mainly cracks in masonry. Relevant hazard estimates for the local, mostly low-rise buildings are given in terms of Peak Ground Velocity (PGV) or the maximum in the 50% damped response spectra at 10 Hz. For example, above the largest Dutch gas field, the Groningen field, we expect that peak values of 20 and 30 mm/s may be exceeded with a 10% probability in 1 and 10 years, respectively. Above some small (about 3–4 km 2) gas fields, Roswinkel and Bergermeer, we expect values around 35 and 60 mm/s, respectively. These values, which exceed the Dutch building research (SBR) vibration guidelines, are obtained using simple model assumptions and are accompanied by an uncertainty analysis. The PSHA provides an important additional insight for the decision maker as to which relevant uncertainties may be decreased and which not. This information can be and is being used to set research and monitoring priorities.

Interrelation among several important links in seismic risk analysis

In order to further reveal the interrelation among division of seismic statistical regions, delimitation of potential seismic sources and estimation of seismicity parameters, we select 21 representative sites located in different places within the range of 100°∼120°E, 29°∼42°N to study the influences of seismicity parameter uncertainties of statistical regions on seismic risk estimations of these sites in the inhomogeneous and homogeneous distribution models. Combining the results from this study and previous ones, we can see that different schemes for dividing seismic statistical regions can change the seismic data in a statistical region. The uncertain data and additional uncertainty in selecting time intervals for seismic statistics will result in uncertainty of seismicity parameters estimation in a statistical region. For the homogeneous model, the larger the variation of this uncertainty is, the greater the uncertain influence on the seismic risk estimation of a site will be, which means that the division of seismic statistical regions makes a major contribution. In a seismic statistical region, the delimitation of potential sources and variant weight assignment of spatial distribution functions can raise the estimated values of ground motion parameters in the place where great earthquake might occur and its vicinity. In these places, the influence of uncertainty in potential source delimitation is very obvious, especially on the absolute magnitude of ground motion parameters (e.g., intensity), which means that the link of potential source delimitation makes a major effect. Generally speaking, the link of potential source delimitation affects mainly the sites located in the potential sources with the highest and second-high upper-limit earthquake magnitudes or in the vicinity of those with the highest upper-limit magnitude. While for the sites located in the potential sources with low upper-limit magnitudes, the uncertainty influence of statistical region division is larger than that of potential source delimitation.

Taking apart the Big Pine fault: Redefining a major structural feature in southern California

New mapping along the Big Pine fault trend in southern California indicates that this structural alignment is actually three separate faults, which exhibit different geometries, slip histories, and senses of offset since Miocene time. The easternmost fault, along the north side of Lockwood Valley, exhibits left‐lateral reverse Quaternary displacement but was a north dipping normal fault in late Oligocene to early Miocene time. The eastern Big Pine fault that bounds the southern edge of the Cuyama Badlands is a south dipping reverse fault that is continuous with the San Guillermo fault. The western segment of the Big Pine fault trend is a north dipping thrust fault continuous with the Pine Mountain fault and delineates the northern boundary of the rotated western Transverse Ranges terrane. This redefinition of the Big Pine fault differs greatly from the previous interpretation and significantly alters regional tectonic models and seismic risk estimates. The outcome of this study also demonstrates that basic geologic mapping is still needed to support the development of geologic models.

Interrelation between seismicity parameters and delimiting potential seismic sources in a seismic statistical region and its influence on seismic risk estimation

In the paper, we have discovered the abnormal area distribution features of maximum variation values of ground motion parameter uncertainty with different probabilities of exceedance in 50 years within the range of 100°–120°E, 29°–42°N for the purpose to solve the problem that abnormal areas of maximum variation values of ground motion parameter uncertainties emerge in a certain cities and towns caused by seismicity parameter uncertainty in a seismic statistical region in an inhomogeneous distribution model that considers tempo-spatial nonuniformity of seismic activity. And we have also approached the interrelation between the risk estimation uncertainty of a site caused by seismicity parameter uncertainty in a seismic statistical region and the delimitation of potential sources, as well as the reasons for forming abnormal areas. The results from the research indicate that the seismicity parameter uncertainty has unequal influence on the uncertainty of risk estimation at each site in a statistical region in the inhomogeneous distribution model, which relates to the scheme for delimiting potential sources. Abnormal areas of maximum variation values of ground motion parameter uncertainty often emerge in the potential sources of M u≥8 (M u is upper limit of a potential source) and their vicinity. However, this kind of influence is equal in the homogeneous distribution model. The uncertainty of risk estimation of each site depends on its seat. Generally speaking, the sites located in the middle part of a statistical region are only related to the seismicity parameter uncertainty of the region, while the sites situated in or near the juncture of two or three statistical regions might be subject to the synthetic influences of seismicity parameter uncertainties of several statistical regions.

Simplified Estimation of Economic Seismic Risk for Buildings

A seismic risk assessment is often performed on behalf of a buyer of commercial buildings in seismically active regions. One outcome of the assessment is that a probable maximum loss ( PML) is computed. PML is of limited use to real-estate investors as it has no place in a standard financial analysis and reflects too long a planning period. We introduce an alternative to PML called probable frequent loss ( PFL), defined as the mean loss resulting from shaking with 10% exceedance probability in 5 years. PFL is approximately related to expected annualized loss ( EAL) through a site economic hazard coefficient (H) introduced here. PFL and EAL offer three advantages over PML: (1) meaningful planning period; (2) applicability in financial analysis (making seismic risk a potential market force); and (3) can be estimated using a single linear structural analysis, via a simplified method called linear assembly-based vulnerability (LABV) that is presented in this work. We also present a simple decision-analysis framework for real-estate investments in seismic regions, accounting for risk aversion. We show that market risk overwhelms uncertainty in seismic risk, allowing one to consider only expected consequences in seismic risk. We illustrate using 15 buildings, including a 7-story nonductile reinforced-concrete moment-frame building in Van Nuys, California, and 14 buildings from the CUREE-Caltech Woodframe Project.

Characteristics of the seismic quiescence and activation patterns before the M=7.2 Kobe earthquake, January 17, 1995

We investigated the characteristics of the seismicity changes associated with the M=7.2 Kobe (Japan) earthquake, January 17, 1995 by applying the Region–Time–Length (RTL) algorithm to the earthquake catalog of the Japan meteorological agency (JMA). The weighted coefficients associated with all three parameters (time, place and magnitude) of earthquakes are taken into account in this algorithm. The JMA catalog after eliminating aftershocks is complete for events with M≥3 in most parts of the Japanese islands during 1977–1995. The RTL parameters at the epicenter indicated that a seismic quiescence (a decrease of seismicity compared to the preceding background rate) started in 1993 and reached its bottom in May 1994. An activation stage (an increase of seismicity compared to the preceding background rate) with duration of about seven months followed. Our detailed investigations indicated that the RTL anomaly during 1993–1994 would not be an artificial effect due to the influence of the changes of some threshold parameters or the changes of the JMA seismological network. The spatial distribution of quiescence during 1993–1994 revealed a significant anomaly in a broad region around the epicenter of the Kobe earthquake. Following the quiescence stage, an activation zone, which was in order of the rupture length, was obtained around the epicenter during May–December 1994. The evolutions of spatial distributions of seismic quiescence and activation suggested that above anomalies around the epicentral zone would have reasonable correlation with the preparation of the Kobe earthquake. The primary characteristics of the seismicity changes prior to the Kobe earthquake are similar to those obtained for other large earthquakes in Kamchatka and Hokkaido. Therefore, the seismicity changes revealed in this study may give better understanding of the seismogenic process of the Kobe earthquake and provide useful information for seismic risk estimation.

都市直下地震を想定した入力地震動の考え方と地域防災計画への指針 : 震源パラメータの不確定性がもたらす地震動入力及び被害評価への影響

Near field earthquakes bring catastrophic disasters in large urbanized cities. Local governments must prepare the regional mitigation plans on the basis of seismic hazard and risk estimation in order to proted the building environment and the population. In case of Sapporo City, that is our research target, it is difficult to specify the source parameters of near field earthquakes affected the populated area. It is necessary to investigate the influence of indefinite parameters upon the risk assessment. In this paper, we enforce an importance of the plural estimation of seismic damages by probable earthquakes occurring near the urban area. Paying attention to the difficulties of taking measures against all of the cases on estimated damages, we give an example of the rule of making decision about the priority of mitigation plans from the point of view of earthquake engineering and political science.

Seismic diffracted waves from topography using 3-D discrete wavenumber‐boundary integral equation simulation

Compressional (P) and shear (S) wave diffraction by free‐surface topography plays a prominent part in the prediction of site responses for seismic risk estimation. Wave propagation modeling in 3-D media is required for an accurate estimation of these diffractions. We have extended the discrete wavenumber‐indirect boundary integral equation method for a 3-D geometry in the case of irregular topography. The Green’s functions are expressed as finite sums of analytical density functions over the horizontal wavenumbers using the spatial periodicity of the topography and a discretization of the surface. We show that the evaluation over vertical wavenumber [Formula: see text] of the analytical integral is possible because a new factor in 1/k2exists. When the force point and the receiver point are at the same vertical position, we develop a numerical strategy to choose the sign of the exponential factor, which is not given by the analytical formulation. The free‐stress boundary conditions at the topography lead to a large linear system that can be solved to obtain the source density functions. Knowing these source density functions, we can compute the diffracted wavefield anywhere inside the medium. We have determined a useful optimal, imaginary frequency to obtain the displacement directly in the frequency domain, avoiding the necessity of returning to the time domain. We have then applied this method to investigate the effect of topography on the ground motion produced by a vertical incident P- or S-wavefield. Waveforms obtained for various topographic steepnesses and shapes show deterministic correlations between the maximum amplitude zone, the geometry of the 3-D topography, and the P- or S-wave incident field characteristics. The maximum amplitude of the diffracted displacement is found near topographic zones that have horizontal or vertical dimensions closely related to the wavelength of the incident field. The predicted ground motion maximal amplifications are twice those calculated in the case of a flat topography.

Intraplate seismicity and zonation

Significant intraplate earthquakes have been observed under deep oceans and in all continents except Greenland. They present special problems of seismic risk estimation compared to the more frequent interplate earthquakes. Their location in space and time is more uncertain because of the low seismicity rate, scattered locations, and lack of surface seismogenic fault evidence. Nevertheless, recent geological and seismological work in several stable continents, particularly western North America and Australia, has improved the assessment of seismic hazard maps and risk zonation in such regions. Estimation of robust synthetic ground motion spectra and time histories, however, remains relatively uncertain. Strong motion instrumentation at Continental Reference Stations (CRS) is recommended.

Modeling of the interaction between destructive inland earthquakes and large off coast earthquakes in central and south-west Japan

A one-dimensional Stick-slip model, which is introduced to explain the fractal features of earthquake phenomena is applied to describe he destructive earthquake occurrences in central and south-west Japan. Space time patterns of events are simulated and the predictablity is discussed. On the basis of the “Block-rotation model”, epicenters of historical destructive earthquakes with magnitude 6.4 or greater are relocated to the tectonic or block boundary lines. This model has revealed that these events show a periodicity of about 1000 years of active and quiet alternative intervals. In each active period, individual block boundary lines generate several large earthquakes without overlapping rupture areas. The space-time pattern and moment release rate for the Hanaore-Kongo Fault Line (HKFL) can be represented well with the one-dimensional stick-slip model. The seismic coupling of large offshore earthquakes along the Nankai trough is also found to be well modeled by this model. This model may be useful for estimation of seismic risk in this region. Further, this model can be applied to see the situation of the M7.2 Kobe earthquake and interpret this earthquake to be the event that comes from the block structure in later section.

Estimation of seismic risk in north-east India: T. Das & S.K. Sarmah, Journal — Assam Science Society, 37(1), 1995, pp 51–55

Estimation of seismic risk in north-east India: T. Das & S.K. Sarmah, Journal — Assam Science Society, 37(1), 1995, pp 51–55

Effect of source depth correction on the estimation of earthquake size

The relationship between surface wave magnitude, Ms, and seismic moment, Mo, of earthquakes is essential for the estimation of seismic risk in any region. In the hypothesis of constant stress drop, theoretical models predict that Log Mo and Ms are related by a linear law. The slope most commonly found in the literature is around 1.5. Here we show that the application to the Ms values of the necessary correction for the focal depth, gives a general increment of the correlation coefficient, and that a slope around 1.0 is consistent with the global data, while for regionalized data it can vary from about 1.0 to 2.0.

Basement seismicity beneath the Andean precordillera thin‐skinned thrust belt and implications for crustal and lithospheric behavior

Data from a digitally recording seismic network in San Juan, Argentina, provide the first images of crustal scale basement faults beneath the Precordillera. This seismicity is near the boundary between the Precordillera (a thin‐skinned thrust belt) and the Sierras Pampeanas (a region of thick‐skinned basement deformation), two seismically active tectonic provinces of the Andean foreland. The seismicity data support models for this region in which crustal thickening, rather than magmatic addition or thermal uplift, plays the dominant mountain building role. The Precordillera seismicity occurs in three segments distributed north to south. The southern segment is an area of diffuse activity extending across the Precordillera and eastward into the Sierras Pampeanas that shows no patterns in map or cross section. The northern and central segments have well‐defined dipping planes that define crustal scale faults extending from 5 to 35 km depth. It is clear from the relative fault geometries that the overlying Precordillera is not simply related to the basement activity. The seismicity here may result from reactivation of an ancient suture between the Precordillera and Pampeanas terranes or be occurring in basement of unknown affinity west of the suture. The seismicity provides the first constraints on basement fault geometries, and we present models integrating this information with the surface geology. These basement faults may have been responsible for the 1944 Ms 7.4 earthquake that destroyed the city of San Juan. The imaging of these faults suggests that seismic risk estimates for San Juan made on the basis of surface geologic studies may be too low.

Recent PRA applications

Seismic risk analysis has become an integral part of Probabilistic Risk Assessment (PRA) of nuclear power plants. To date, there have been over 25 seismic PRAs conducted. More recent emphasis in the performance of seismic PRAs has been on detailed plant review and walkdown, use of insights from past PRAs, development of simplified methods, and detailed systems modeling. In this paper, a review of more recent applications of seismic PRAs is provided. It describes the seismic PRA on a plant performed by a utility, the application of a seismic PRA in the estimation of seismic risk from spent fuel pools, and the development and applications of simplified PRAs by Sandia National Laboratories for USNRC. The focus is on recent methodological developments and data improvements in this area.

Recent extensions to seismic margin review methodology

Two seismic margin review methodologies — one by USNRC and the other by EPRI — have been developed in the last four years. The focus is on assessing the capability of existing nuclear power plants to withstand earthquakes larger than the design basis earthquakes. The methods restrict the analysis to a selected few systems and components using the insights from past seismic PRAs, seismic analysis and qualification results, and earthquake experience data. The objective of this paper is to describe recent and on-going studies in extending the NRC seismic margin review methodology. Specifically, three topics are discussed: (1) extension of the HCLPF capacity to analyse radiological releases and importance of human factors and non-seismic failures; (2) importance of BWR plant systems and functions to seismic margins; and (3) extensions of seismic margin review results to obtain seismic risk estimates.