Search

Twenty papers on the study of tsunamis and respective tsunamigenic earthquakes are included in Volume II of the PAGEOPH topical issue 'Tsunami Science: Ten Years after the 2004 Indian Ocean Tsunami'. The papers presented in this second of two special volumes of Pure and Applied Geophysics reflect the state of tsunami science during this time, including five papers devoted to new findings specifically in the Indian Ocean. Two papers compile results from global observations and eight papers cover Pacific Ocean studies, focusing mainly on the 2011 Tohoku earthquake and tsunami. Remaining papers in this volume describe studies in the Atlantic Ocean and Mediterranean Sea and tsunami source studies. Overall, the volume not only addresses the pivotal 2004 Indian Ocean and 2011 Tohoku tsunamis, but also examines the tsunami hazard posed to other critical coasts in the world. [ABSTRACT FROM AUTHOR]

Two large earthquakes occurred in the western part of China in 2008, one of them being the Yutian (35.6°N, 81.6°E) M7.3 earthquake that occurred on March 21 (BJT) and the other the Wenchuan (31.0°N, 103.4°E) M8.0 earthquake that occurred on May 12 (BJT). In this paper, the West Continental China (included in 20.0°-50.0°N, 70.0°-110.0°E region) was the study region for verifyong the predictability of the pattern informatics (PI) method using the receiver-operating characteristic curve (ROC) test and R score test. Different forecasting maps with different calculating parameters were obtained. The calculating parameters were the grid size Δ x, base time t, reference interval t to t, change interval t to t, and forecasting interval t to t. In this paper, the base time t fixed to June 1, 1971, the ending forecast time t fixed to June 1, 2008, and the forecasting interval t to t changed from 1 to 10 years, and the grid sizes were chosen as 1° × 1° and 2° × 2°, respectively. The results show that the PI method could forecast the Yutian M7.3 and Wenchuan M8.0 earthquakes only using suitable parameters. Comparing the forecast results of grid sizes 1° × 1° and 2° × 2°, the models with 2° × 2° grids were better. Comparing the forecast results with different forecasting windows from 1 to 10 years, the models with forecasting windows of 4-8 years were better using the ROC test, and the models with forecasting windows of 7-10 years were better using the R score test. The forecast efficiency of the model with a grid size of 2° × 2° and forecast window of 8 years was the best one using either the ROC test or the R score test. [ABSTRACT FROM AUTHOR]

The evolution laws of LURR (Loading-Unloading Response Ratio) before strong earthquakes, especially the peak point of LURR, are described in this paper. The results of four methods (experimental, numerical simulation, seismic data analysis and with damage mechanics analysis) lead to a consistent conclusion-the evolution laws of LURR before strong earthquakes are that, at the early stage of the seismic cycle, LURR will fluctuate around 1 and in the late stage, it rises swiftly and to its peak point. At some time after this peak point, a catastrophic event or events occur. These do not occur at the peak point, but lag behind. The lag time which is denoted by T depends on the magnitude M of the upcoming earthquake among other factors. In order to consider the influence of geophysical parameters in a specific region such as $$ \dot{\gamma }, $$ E and J, where $$ \dot{\gamma } $$ is the shear strain rate of tectonic loading in situ, E is the sum of radiated energy of all earthquake occurring in a specific region measured during a long time duration (110 years in this paper) divided by the area of the region and the time duration, and J is a parameter denoting the LURR anomaly area weighted with Y (the value of LURR) and represents the expanse and degree of the seismogenic zone. The dimensional analysis method has been used to reveal the relation between M, T and other parameters in situ for more reliable earthquake prediction. [ABSTRACT FROM AUTHOR]

Crustal gravitational potential energy (GPE) change induced by earthquakes is an important subject in geophysics and seismology. For the past forty years the research on this subject stayed in the stage of qualitative estimate. In recent few years the 3D dynamic faulting theory provided a quantitative solution of this subject. The theory deduced a quantitative calculating formula for the crustal GPE change using the mathematic method of tensor analysis under the principal stresses system. This formula contains only the vertical principal stress, rupture area, slip, dip, and rake; it does not include the horizontal principal stresses. It is just involved in simple mathematical operations and does not hold complicated surface or volume integrals. Moreover, the hanging wall vertical moving (up or down) height has a very simple expression containing only slip, dip, and rake. The above results are significant to investigate crustal GPE change. Commonly, the vertical principal stress is related to the gravitational field, substituting the relationship between the vertical principal stress and gravitational force into the above formula yields an alternative formula of crustal GPE change. The alternative formula indicates that even with lack of in situ borehole measured stress data, scientists can still quantitatively calculate crustal GPE change. The 3D dynamic faulting theory can be used for research on continental fault earthquakes; it also can be applied to investigate subduction earthquakes between oceanic and continental plates. Subduction earthquakes hold three types: (a) crust only on the vertical up side of the rupture area; (b) crust and seawater both on the vertical up side of the rupture area; (c) crust only on the vertical up side of the partial rupture area, and crust and seawater both on the vertical up side of the remaining rupture area. For each type we provide its quantitative formula of the crustal GPE change. We also establish a simplified model (called CRW Model) as follows: for Type B and Type C subduction earthquakes, if the seawater average depth on the vertical up side of the rupture area is less than a tenth of the hypocenter depth, then take the approximation that the seawater above the continental plate is replaced by the upper crustal material of the continental plate. The formula of quantitative calculating the crustal GPE change is also provided for this model. Finally, for 16 September 2015 Mw 8.3 Illapel Chile earthquake, we apply CRW Model and obtain the following results: the crustal GPE change is equal to 1.8 × 10 J, and the hanging wall vertical moving-up height is 1.9 m with respect to the footwall. We believe this paper might be the first report on the quantitative solution of the crustal GPE change for this subduction earthquake; our results and related method will be helpful in research into the earthquakes in Peru-Chile subduction zone and the Andean orogeny. In short, this study expounds a new method for quantitative determining the crustal GPE change caused by subduction earthquakes, which is different from other existing methods. [ABSTRACT FROM AUTHOR]

The 16 September 2015 Illapel, Chile, earthquake and associated tsunami have been studied by many researchers from various aspects. This paper reviews studies on the source model of the earthquake and examines tsunami data. The Illapel earthquake occurred in the source region of previous earthquakes in 1943 and 1880. The earthquake source was studied using various geophysical data, such as near-field seismograms, teleseismic waveform and backprojection, GPS and InSAR data, and tsunami waveforms. Most seismological analyses show a duration of ~100 s with a peak at ~50 s. The spatial distribution has some variety, but they all have the largest slip varying from 5 to 16 m located at 31°S, 72°W, which is ~70 km NW of the epicenter. The shallow slip seems to be extended to the trench axis. A deeper slip patch was proposed from high-frequency seismic data. A tsunami earthquake model with a total duration of 250 s and a third asperity south of the epicenter is also proposed, but we show that the tsunami data do not support this model. [ABSTRACT FROM AUTHOR]

Heavy tailed random variables (rvs) have proven to be an essential element in modeling a wide variety of natural and human-induced processes, and the sums of heavy tailed rvs represent a particularly important construction in such models. Oriented toward both geophysical and statistical audiences, this paper discusses the appearance of the Pareto law in seismology and addresses the problem of the statistical approximation for the sums of independent rvs with common Pareto distributionF(x)=1 -x-a for 1/2

— The Indo-Burma (Myanmar) subduction boundary is highly oblique to the direction of relative velocity of the Indian tectonic plate with respect to the Eurasian plate. The area includes features of active subduction zones such as a Wadati-Benioff zone of earthquakes, a magmatic arc, thrust and fold belts. It also has features of oblique subduction such as: an arc-parallel strike-slip fault (Sagaing Fault) that takes up a large fraction of the northward component of motion and a buttress (the Mishmi block) that resists the motion of the fore-arc sliver. In this paper, I have examined the seismicity, slip vectors and principal axes of the focal mechanisms of the earthquakes to look for features of active subduction zones and for evidence of slip partitioning as observed in other subduction zones. The data set consists of Harvard CMT solutions of 89 earthquakes (1977–1999 with 4.8≦̸Mw≦̸7.2 and depths between 3–140 km). Most of these events are shallow and intermediate depth events occurring within the Indian plate subducting eastward beneath the Indo-Burman ranges. Some shallow events within the fore-arc region have arc-parallel Paxes, reflecting buttressing of the fore-arc sliver at its leading edge. Some of the shallowest events have nearly E-W oriented P axes which might account for recent folding and thrusting. Examination of earthquake slip vectors in this region shows that the slip vector azimuths of earthquakes in the region between 20°–26°N are rotated towards the trench normal, which is an indication of partial partitioning of the oblique convergence. It is seen that all aspects of seismicity, including the paucity of shallow underthrusting earthquakes and the orientation of P axes, are consistent with oblique convergence. The conclusions of this paper are consistent with recent geological studies and interpretations such as the coexistence of eastward subduction, volcanic activity and transcurrent movement through mid-Miocene to Quaternary period. [ABSTRACT FROM AUTHOR]

— The problem of the coseismic deformation induced by an earthquake on its own fault plane is investigated here. The analysis concentrates on the on-fault displacement field accompanying the occurrence of an earthquake in response to a prescribed uniform shear slip and it is carried out on the basis of the classical analytical model by Okada (1992) for a rectangular fault buried in an elastic homogeneous half-space delimited by a planar free surface. The analysis is subdivided into two separate papers: the first dealing with normal and the second with tangential on-fault displacements. In this first paper, concerning the study of the normal displacement component, the contributions of the source and of the correction introduced by the free surface are investigated separately and their dependence on the fault characteristics is thoroughly discussed. Particular attention is also devoted to the effects of the normal displacement on the fault surface geometry. It will be shown that the main effect is that of deforming the fault itself, with deformation consisting chiefly in a rotation of the plane and in a bending of the fault edges. The rotation angle is negligibly small (on the order of 1–10 μrad) for a single earthquake, although repeated seismic events occurring on the same fault might result in rotations of several degrees over geological time scales. [ABSTRACT FROM AUTHOR]

— This paper regards the on-fault displacement field generated by an earthquake on its own fault plane, with special attention to the tangential displacement vector. It is the continuation and the completion of a previous paper (Armigliato et al., 2003) concerning the analysis of the normal on-fault displacement component. It is here recognised that in addition to the discontinuous shear displacement, which is the main contribution to the seismic dislocation on the fault, there is a tangential displacement contribution that is continuous across the fault. The continuous tangential displacement is exclusively produced by the presence of the free earth's surface. The tangential displacement vector has non-vanishing components in both directions, parallel as well as perpendicular to the imposed uniform shear slip, the first being predominant on the second. We perform a set of computations aimed at evaluating the dependence of the tangential displacement magn itude on the relevant fault parameters for basic cases of rectangular faults embedded in a homogeneous half-space. [ABSTRACT FROM AUTHOR]

Izmir, the third largest city and one of the major economic centers in Turkey, has more than three million residents and one-half million buildings. The city, located in a seismically active region in western Anatolia, was a subject of the 1997 RADIUS (Risk Assessment Tools for Diagnosis of Urban Areas against Seismic Disaster) project. In this paper, the seismic hazard of Izmir is investigated through probabilistic seismic hazard assessment. First, the seismic setting of Izmir is presented. Considering the statistics of earthquakes that took place in the region during the period 1900-2005, a simple seismic hazard model is used to facilitate the assessment. To account for modeling uncertainties associated with the values of seismicity parameters, a logic tree procedure is employed in carrying out the seismic hazard computations. The resulting weighted average seismic hazard, presented in terms of peak ground acceleration and associated probability of exceedence, could be considered the 'best estimate' of seismic hazard for Izmir. Accordingly, for a return period of 475 years, for rock sites, a PGA value of 0.34 g is calculated. This PGA hazard estimate is close to the current code-recommended design acceleration level for Izmir. [ABSTRACT FROM AUTHOR]

In this paper, ground motion during the Independence Day earthquake of August 15, 1950 (Mw 8.6, B en-M enahem et al., 1974) in the northeastern part of India is estimated by seismological approaches. A hybrid simulation technique which combines the low frequency ground motion simulated from an analytical source mechanism model with the stochastically simulated high-frequency components is used for obtaining the acceleration time histories. A series of ground motion simulations are carried out to estimate the peak ground acceleration (PGA) and spectral accelerations at important cities and towns in the epicentral region. One sample PGA distribution in the epicentral region encompassing the epicenter is also obtained. It is found that PGA in the epicentral region has exceeded 1 g during this earthquake. The estimated PGA’s are validated to the extent possible using the MMI values. The simulated acceleration time histories can be used for the assessment of important engineering structures in northeastern India. [ABSTRACT FROM AUTHOR]

The article presents a list of published papers authored or co-authored by geophysicist Keiiti Aki. Periodical articles the list include "Quantitative prediction of earthquake occurrence as stochastic phenomena," "Thermal processes near the earth's crust," "Relay computer for correlogram analysis," and "Correlogram analysis of seismograms."

- An algorithm recently developed by RUNDLEet al. (2002) to find regions of anomalous seismic activity associated with large earthquakes identified the location of anM w = 5.6 earthquake near Calexico, Mexico. In this paper we analyze the regional seismicity before this event, and a nearbyM w = 5.7 event, using time-to-failure algorithms developed by BOWMANet al. (1998) and BOWMAN and KING (2001a,b). The former finds the radius of a circular region surrounding the epicenter that optimizes the time-to-failure acceleration of seismic release. The latter optimizes acceleration based on the expected stress accumulation pattern for a dislocation source. Both methods found a period of accelerating seismicity in an optimal region, the size of which agrees with previously proposed scaling relations. This positive result suggests that the Rundle algorithm may provide a useful technique to identify regions of accelerating seismicity, which can then be analyzed using signal optimization time-to-failure techniques. [ABSTRACT FROM AUTHOR]

— The study of surface deformation due to seismic activity is often made using dislocations with uniform slip and simple geometries. A better modeling of coseismic and postseismic surface displacements can be obtained by using dislocations with variable slip and nonregular shapes. This is consistent with the asperity model of fault surfaces, assuming a friction distribution on faults made of locked zones with much higher friction than surrounding zones. In this paper we consider the 1997–1998 Colfiorito seismic sequence. The coseismic surface displacements in the Colfiorito zone are used in order to infer the slip distribution on the fault surface at different stages of the sequence. The displacement field has been modeled varying the slip distribution on the fault, and comparing the deformation observed by SAR and GPS techniques with model results. The slip distribution is calculated by Monte Carlo simulations on a normal fault with the dip angle equal to 40°. A good approximation is obtained by using square asperity units of 1.5×1.5 km2. In the first stage, we employed a simplified model with uniform slip, in which each asperity unit is allowed to slip a constant amount or not to slip at all, and in the second stage, we evaluate the slip distribution in the dislocation area determined by the Monte Carlo inversion: in this case we allow unit cells to undergo different values of slip in order to refine the initial dislocation model. The results show that the 1997 seismic events of the sequence can be modeled by irregular dislocations, obtaining a good fit to the DInSAR and GPS observations. The model also confirms the results of previous studies by a different methodology, defining the distribution of asperities on the fault plane using the fault geometry, the geodetic data and the seismic moment of the 1997–1998 Colfiorito seismic sequence. Furthermore, the analysis of 1997 aftershocks in the seismogenic region shows a strong correlation between most events and the asperity distribution, which can be considered as an independent test of the validity of the model. [ABSTRACT FROM AUTHOR]