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Large Earthquakes (large + earthquake)
Selected AbstractsLarge earthquakes and the abandonment of prehistoric coastal settlements in 15th century New ZealandGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 6 2003James R. Goff This paper reports on the effects of large earthquakes and related events, such as tsunamis, on prehistoric coastal settlements in New Zealand. It is based on field observations at several well-established archaeological sites around the Cook Strait region and on literature reviews. We identify three broad periods of seismic activity in New Zealand since human occupation of the islands: 13th century, 15th century, and the 1750s to 1850s. The most significant, from a prehistoric human perspective, is the 15th century. Using examples from the Cook Strait region, we suggest that the abandonment of coastal settlements, the movement of people from the coast to inland areas, and a shift in settlement location from sheltered coastal bays to exposed headlands, was due to seismic activity, including tsunamis. We expect similar patterns to have occurred in other parts of New Zealand, and other coastal areas of the world with longer occupation histories. © 2003 Wiley Periodicals, Inc. [source] A probabilistic approach for earthquake potential evaluation based on the load/unload response ratio methodCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 12 2010Huai-Zhong Yu Abstract Previous studies indicate that the occurrence of a large earthquake might be predicted by anomalous temporal increase of the load/unload response ratio (LURR), which was often defined as the ratio of Benioff strain of small earthquakes released during loading and unloading time periods, corresponding to earth tide-induced Coulomb failure stress change on optimally oriented faults. The conventional LURR anomalous evaluation usually sets a critical LURR value, above which an earthquake may occur. In this paper a probabilistic approach for the evaluation of earthquake potential based on the LURR method is developed. In the approach, the occurrence probability of a future earthquake is quantitatively evaluated by assessing the confidence level of LURR anomaly associated with its stochastic distribution. As retrospective studies, we apply the approach to investigate the time series of LURR prior to the 50M>6.3 earthquakes that occurred in the Chinese mainland and the 21M>6.0 earthquakes in southern California over the past 30 years, and find high correlation between the confidence level of the LURR anomalies and the occurrence of the large earthquakes. We then depict all the high peaks that appeared in the LURR time series, and evaluate the earthquake occurrence rate as a function of the confidence level. The research results show considerable promise that our probabilistic approach may provide a useful tool to evaluate quantitatively the occurrence possibilities of future earthquakes. Copyright © 2009 John Wiley & Sons, Ltd. [source] Effects of earthquake and cyclone sequencing on landsliding and fluvial sediment transfer in a mountain catchmentEARTH SURFACE PROCESSES AND LANDFORMS, Issue 9 2008Guan-Wei Lin Abstract Patterns and rates of landsliding and fluvial sediment transfer in mountain catchments are determined by the strength and location of rain storms and earthquakes, and by the sequence in which they occur. To explore this notion, landslides caused by three tropical cyclones and a very large earthquake have been mapped in the Chenyoulan catchment in the Taiwan Central Range, where water and sediment discharges and rock strengths are well known. Prior to the MW 7·6 Chi-Chi earthquake in 1999, storm-driven landslide rates were modest. Landslides occurred primarily low within the landscape in shallow slopes, reworking older colluvial material. The Chi-Chi earthquake caused wide-spread landsliding in the steepest bedrock slopes high within the catchment due to topographic focusing of incoming seismic waves. After the earthquake landslide rates remained elevated, landslide patterns closely tracking the distribution of coseismic landslides. These patterns have not been strongly affected by rock strength. Sediment loads of the Chenyoulan River have been limited by supply from hillslopes. Prior to the Chi-Chi earthquake, the erosion budget was dominated by one exceptionally large flood, with anomalously high sediment concentrations, caused by typhoon Herb in 1996. Sediment concentrations were much higher than normal in intermediate size floods during the first 5 years after the earthquake, giving high sediment yields. In 2005, sediment concentrations had decreased to values prevalent before 1999. The hillslope response to the Chi-Chi earthquake has been much stronger than the five-fold increase of fluvial sediment loads and concentrations, but since the earthquake, hillslope sediment sources have become increasingly disconnected from the channel system, with 90 per cent of landslides not reaching into channels. Downslope advection of landslide debris associated with the Chi-Chi earthquake is driven by the impact of tropical cyclones, but occurs on a time-scale longer than this study. Copyright © 2008 John Wiley & Sons, Ltd. [source] A neural network approach for structural identification and diagnosis of a building from seismic response dataEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 2 2003C. S. Huang Abstract This work presents a novel procedure for identifying the dynamic characteristics of a building and diagnosing whether the building has been damaged by earthquakes, using a back-propagation neural network approach. The dynamic characteristics are directly evaluated from the weighting matrices of the neural network trained by observed acceleration responses and input base excitations. Whether the building is damaged under a large earthquake is assessed by comparing the modal parameters and responses for this large earthquake with those for a small earthquake that has not caused this building any damage. The feasibility of the approach is demonstrated through processing the dynamic responses of a five-storey steel frame, subjected to different strengths of the Kobe earthquake, in shaking table tests. Copyright © 2002 John Wiley & Sons, Ltd. [source] Dissecting large earthquakes in Japan: Role of arc magma and fluidsISLAND ARC, Issue 1 2010Dapeng Zhao Abstract We synthesized information from recent high-resolution tomographic studies of large crustal earthquakes which occurred in the Japanese Islands during 1995,2008. Prominent anomalies of low-velocity and high Poisson's ratio are revealed in the crust and uppermost mantle beneath the mainshock hypocenters, which may reflect arc magma and fluids that are produced by a combination of subducting slab dehydration and corner flow in the mantle wedge. Distribution of 164 crustal earthquakes (M 5.7,8.0) that occurred in Japan during 1885,2008 also shows a correlation with the distribution of low-velocity zones in the crust and uppermost mantle. A qualitative model is proposed to explain the geophysical observations recorded so far in Japan. We consider that the nucleation of a large earthquake is not entirely a mechanical process, but is closely related to the subduction dynamics and physical and chemical properties of materials in the crust and upper mantle; in particular, the arc magma and fluids. [source] A probabilistic approach for earthquake potential evaluation based on the load/unload response ratio methodCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 12 2010Huai-Zhong Yu Abstract Previous studies indicate that the occurrence of a large earthquake might be predicted by anomalous temporal increase of the load/unload response ratio (LURR), which was often defined as the ratio of Benioff strain of small earthquakes released during loading and unloading time periods, corresponding to earth tide-induced Coulomb failure stress change on optimally oriented faults. The conventional LURR anomalous evaluation usually sets a critical LURR value, above which an earthquake may occur. In this paper a probabilistic approach for the evaluation of earthquake potential based on the LURR method is developed. In the approach, the occurrence probability of a future earthquake is quantitatively evaluated by assessing the confidence level of LURR anomaly associated with its stochastic distribution. As retrospective studies, we apply the approach to investigate the time series of LURR prior to the 50M>6.3 earthquakes that occurred in the Chinese mainland and the 21M>6.0 earthquakes in southern California over the past 30 years, and find high correlation between the confidence level of the LURR anomalies and the occurrence of the large earthquakes. We then depict all the high peaks that appeared in the LURR time series, and evaluate the earthquake occurrence rate as a function of the confidence level. The research results show considerable promise that our probabilistic approach may provide a useful tool to evaluate quantitatively the occurrence possibilities of future earthquakes. Copyright © 2009 John Wiley & Sons, Ltd. [source] Statistical performance analysis of seismic-excited structures with active interaction controlEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 7 2003Yunfeng Zhang Abstract This paper presents a statistical performance analysis of a semi-active structural control system for suppressing the vibration response of building structures during strong seismic events. The proposed semi-active mass damper device consists of a high-frequency mass damper with large stiffness, and an actively controlled interaction element that connects the mass damper to the structure. Through actively modulating the operating states of the interaction elements according to pre-specified control logic, vibrational energy in the structure is dissipated in the mass damper device and the vibration of the structure is thus suppressed. The control logic, categorized under active interaction control, is defined directly in physical space by minimizing the inter-storey drift of the structure to the maximum extent. This semi-active structural control approach has been shown to be effective in reducing the vibration response of building structures due to specific earthquake ground motions. To further evaluate the control performance, a Monte Carlo simulation of the seismic response of a three-storey steel-framed building model equipped with the proposed semi-active mass damper device is performed based on a large ensemble of artificially generated earthquake ground motions. A procedure for generating code-compatible artificial earthquake accelerograms is also briefly described. The results obtained clearly demonstrate the effectiveness of the proposed semi-active mass damper device in controlling vibrations of building structures during large earthquakes. Copyright © 2003 John Wiley & Sons, Ltd. [source] Large earthquakes and the abandonment of prehistoric coastal settlements in 15th century New ZealandGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 6 2003James R. Goff This paper reports on the effects of large earthquakes and related events, such as tsunamis, on prehistoric coastal settlements in New Zealand. It is based on field observations at several well-established archaeological sites around the Cook Strait region and on literature reviews. We identify three broad periods of seismic activity in New Zealand since human occupation of the islands: 13th century, 15th century, and the 1750s to 1850s. The most significant, from a prehistoric human perspective, is the 15th century. Using examples from the Cook Strait region, we suggest that the abandonment of coastal settlements, the movement of people from the coast to inland areas, and a shift in settlement location from sheltered coastal bays to exposed headlands, was due to seismic activity, including tsunamis. We expect similar patterns to have occurred in other parts of New Zealand, and other coastal areas of the world with longer occupation histories. © 2003 Wiley Periodicals, Inc. [source] Mechanical deformation model of the western United States instantaneous strain-rate fieldGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2006Fred F. Pollitz SUMMARY We present a relationship between the long-term fault slip rates and instantaneous velocities as measured by Global Positioning System (GPS) or other geodetic measurements over a short time span. The main elements are the secularly increasing forces imposed by the bounding Pacific and Juan de Fuca (JdF) plates on the North American plate, viscoelastic relaxation following selected large earthquakes occurring on faults that are locked during their respective interseismic periods, and steady slip along creeping portions of faults in the context of a thin-plate system. In detail, the physical model allows separate treatments of faults with known geometry and slip history, faults with incomplete characterization (i.e. fault geometry but not necessarily slip history is available), creeping faults, and dislocation sources distributed between the faults. We model the western United States strain-rate field, derived from 746 GPS velocity vectors, in order to test the importance of the relaxation from historic events and characterize the tectonic forces imposed by the bounding Pacific and JdF plates. Relaxation following major earthquakes (M, 8.0) strongly shapes the present strain-rate field over most of the plate boundary zone. Equally important are lateral shear transmitted across the Pacific,North America plate boundary along ,1000 km of the continental shelf, downdip forces distributed along the Cascadia subduction interface, and distributed slip in the lower lithosphere. Post-earthquake relaxation and tectonic forcing, combined with distributed deep slip, constructively interfere near the western margin of the plate boundary zone, producing locally large strain accumulation along the San Andreas fault (SAF) system. However, they destructively interfere further into the plate interior, resulting in smaller and more variable strain accumulation patterns in the eastern part of the plate boundary zone. Much of the right-lateral strain accumulation along the SAF system is systematically underpredicted by models which account only for relaxation from known large earthquakes. This strongly suggests that in addition to viscoelastic-cycle effects, steady deep slip in the lower lithosphere is needed to explain the observed strain-rate field. [source] Seismic activity triggered by the 1999 Izmit earthquake and its implications for the assessment of future seismic riskGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2001Ali Pinar Summary A serious question has remained as to the location of the western end of the main rupture zone associated with the 1999 Izmit, Turkey, earthquake. A clear answer to this question is extremely important for the assessment of future seismic risk in the eastern Marmara Sea region, Turkey. In this paper we show an effective approach to answering this important question, unifying different kinds of information such as seismic activity, focal mechanism solutions and stress changes caused by the main shock into a clear image. We first point out that the major moment release is 1.6 × 1020 N m and covered the area between 29.7°E and 30.5°E and we then claim that the enhanced seismic activity after the main shock in the eastern Marmara Sea region should be regarded as activity triggered by the increase of stress, rather than as aftershock activity along the ruptured zone. We propose three fault segments with an average stress increase on each in the western extension of the main-shock rupture zone as potential sites for future large earthquakes, namely (i) the 50 km long Yalova,Hersek segment (0.45 MPa), (ii) the NW,SE-trending right-lateral strike-slip fault known as the Princes Islands segment (0.18 MPa), and (iii) the Çinarcik,Yalova segment (0.09 MPa) characterized by normal faulting, which was subject to rupture in 1963. [source] A cyclic viscoelastic,viscoplastic constitutive model for clay and liquefaction analysis of multi-layered groundINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 2 2004Fusao Oka Abstract In order to estimate viscous effect of clay in the wide range of low to high level of strain, a cyclic viscoelastic,viscoplastic constitutive model for clay is proposed. First, we confirm the performance of the proposed model by simulating the cyclic undrained triaxial tests to determine the cyclic strength and deformation characteristics of a natural marine clay. Then, the proposed model is incorporated into an effective stress based liquefaction analysis method to estimate the effect of an intermediate clay layer on the behaviour of liquefiable sand layers. The seismic response against foreshocks, main shock as well as aftershocks of 1995 Hyogoken Nambu Earthquake is analysed in the present study. The difference of shear strength characteristics of the alluvial clay layer is one of the reasons why Port Island has a higher liquefaction potential than that of Rokko Island. The proposed model gives a good description of the damping characteristics of clay layer during large earthquakes. Acceleration responses in both clay layer and liquefiable sand layer just above it are damped due to viscous effect of clay. In the case of main shock and the following aftershocks that occurred within less than 9 days after main event, acceleration responses near ground surface are de-amplified due to the developed excess pore water pressure, while responses near ground surface are amplified before and long after the main event. Using the viscoelastic,viscoplastic model for clay layer, time history of acceleration response in upper liquefiable sand layer can be well calculated, in particular in the range of microtremor process after the main seismic motion. Copyright © 2004 John Wiley & Sons, Ltd. [source] Dissecting large earthquakes in Japan: Role of arc magma and fluidsISLAND ARC, Issue 1 2010Dapeng Zhao Abstract We synthesized information from recent high-resolution tomographic studies of large crustal earthquakes which occurred in the Japanese Islands during 1995,2008. Prominent anomalies of low-velocity and high Poisson's ratio are revealed in the crust and uppermost mantle beneath the mainshock hypocenters, which may reflect arc magma and fluids that are produced by a combination of subducting slab dehydration and corner flow in the mantle wedge. Distribution of 164 crustal earthquakes (M 5.7,8.0) that occurred in Japan during 1885,2008 also shows a correlation with the distribution of low-velocity zones in the crust and uppermost mantle. A qualitative model is proposed to explain the geophysical observations recorded so far in Japan. We consider that the nucleation of a large earthquake is not entirely a mechanical process, but is closely related to the subduction dynamics and physical and chemical properties of materials in the crust and upper mantle; in particular, the arc magma and fluids. [source] KeyGraph as Risk Explorer in Earthquake,SequenceJOURNAL OF CONTINGENCIES AND CRISIS MANAGEMENT, Issue 3 2002Yukio Ohsawa KeyGraph, a document,indexing (keyword,extraction) algorithm, is applied for a new purpose: Extracting active faults with risks of near,future large earthquakes from earthquake,sequences. This paper presents KeyGraph as an extractor of causalities from an event,sequence. This validates KeyGraph as a tool for showing why and which active faults are risky, as well as for showing why and which words abstract a document. The risky faults that are empirically obtained by KeyGraph correspond closely to real earthquake occurrences and seismologists' risk estimation. [source] | |||||||||||||