Spatial Distribution Of Epicenters Research Articles

Estimation of fractal dimension and b-value of earthquakes in the Himalayan region

The Himalayan belt is known for seismic activities; however, activities across this belt are not uniform due to various factors, including stress regime, heterogeneity of subsurface material, and the manner by which the major tectonic Indian plate is colliding with the Eurasian plate. In this study, three sample regions spanning northwest to northeast Himalayas (Kashmir, Nepal, and northeast Himalayan regions) were selected, and their b-values and fractal dimensions from the investigation period of 1973–2015 were calculated. Subsequently, the b-value was calculated via the Gutenberg–Richter relation and maximum likelihood method, whereas the fractal dimension or D-value was calculated using the correlation integral technique. Upon subdividing the time duration into six equal interval subsets, a variation in b-value can be observed over the years. The period 1973–2015 was selected to ensure the sufficiency of data in each subset and an adequate number of subsets for comparisons. From the low b-values, possible high-stress regions and asperities can be inferred, and the variation in stress and heterogeneity of material can be observed from the northwest to northeast Himalayas. An increase in b-value was observed on moving from the northwest to northeast Himalayas during the period of investigation. From the D-value, the extent of the epicentre cluster was observed, revealing that the epicentres were far more clustered to a point in Nepal Himalayas than in the two other regions. The spatial distribution of epicentres was more or less in 1D (fractal dimension) in the northeast and northwest Himalayas, indicating their distribution along particular geological linear features, such as major faults. Hence, a comparative study of the three regions was achieved. On the basis of the b-value, the types of fault and tectonics can be predicted, and the frequency of earthquakes in these Himalayan regions can be better understood.

Aftershock analysis of the 2015 Gorkha-Dolakha (Central Nepal) earthquake doublet

On 25 April 2015, a large earthquake with moment-magnitude (Mw) 7.8 occurred at Gorkha (latitude 28.23° N and longitude 84.73° E) in Central Nepal. Just 17 days later, another large earthquake of Mw 7.3 occurred at Dolakha (latitude 27.80° N and longitude 86.06° E), about 140 km away from the previous epicenter. In this study, we deal with the aftershocks of these two earthquakes that occurred in the region (27°–28.5°N, 84°–87°E) spanning the period from 25 April 2015 to 28 May 2016 to find the spatiotemporal distribution patterns, the size distribution (b-value), and the aftershock decay rate (p-value) of this sequence. Aftershock epicenters of the 2015 Gorkha-Dolakha earthquake doublet are distributed over an area approximately 170 km in length and 70 km in width and largely confined in a depth range from 5 to 25 km. The spatial distribution of epicenters and known geological structures in this study reveals that aftershocks are limited on the east by the surface trace of the Everest lineament and on the south side by the surface trace of the segment of the Main Boundary Thrust (MBT). The estimated b-and p-values of this seismic sequence are 0.93 ± 0.03 and 0.79 ± 0.24, respectively. This b-value is higher than the b-value estimated by the previous studies, while the p-value corresponds in general with the p-value obtained by recent study in the region.

Multifractal analysis of 2001 [formula omitted] Bhuj earthquake sequence in Gujarat, Western India

The 2001 Mw7.7 Bhuj mainshock seismic sequence in the Kachchh area, occurring during 2001 to 2012, has been analyzed using mono-fractal and multi-fractal dimension spectrum analysis technique. This region was characterized by frequent moderate shocks of Mw≥5.0 for more than a decade since the occurrence of 2001 Bhuj earthquake. The present study is therefore important for precursory analysis using this sequence. The selected long-sequence has been investigated first time for completeness magnitude Mc 3.0 using the maximum curvature method. Multi-fractal Dq spectrum (Dq∼q) analysis was carried out using effective window-length of 200 earthquakes with a moving window of 20 events overlapped by 180 events. The robustness of the analysis has been tested by considering the magnitude completeness correction term of 0.2 to Mc 3.0 as Mc 3.2 and we have tested the error in the calculus of Dq for each magnitude threshold. On the other hand, the stability of the analysis has been investigated down to the minimum magnitude of Mw≥2.6 in the sequence. The analysis shows the multi-fractal dimension spectrum Dq decreases with increasing of clustering of events with time before a moderate magnitude earthquake in the sequence, which alternatively accounts for non-randomness in the spatial distribution of epicenters and its self-organized criticality. Similar behavior is ubiquitous elsewhere around the globe, and warns for proximity of a damaging seismic event in an area. OS: Please confirm math roman or italics in abs.

THE GEOMORPHOLOGIC AFTERMATH OF THE EARTHQUAKE IN GORNY ALTAI

Geomorphologic effects of catastrophic earthquake in Altai Mountains (September 27, 2003) are described. Field investigations have helped to reveal spatial distribution of epicenters and to determine the area of their maximal concentration. The earthquake gave rise to many new landforms: landslides-collapses, chasm-fractures, small “mud-vol-canoes”, soak-holes, screes. The activation of exogenous processes is likely to happen during spring and summer of the year 2004 due to weakening of glaciers and slope deposits caused by earthquakes.

Neotectonics of the Dinarides–Pannonian Basin transition and possible earthquake sources in the Banja Luka epicentral area

This study provides evidence for post-5Ma shortening in the transition area between the Dinarides fold-and-thrust belt and the Pannonian Basin and reviews possible earthquake sources for the Banja Luka epicentral area (northern Bosnia and Herzegovina) where the strongest instrumentally recorded earthquake (ML 6.4) occurred on 27 October 1969. Geological, geomorphological and reflection seismic data provide evidence for a contractional reactivation of Late Palaeogene to Middle Miocene normal faults at slip rates below 0.1mm/a. This reactivation postdates deposition of the youngest sediments in the Pannonian Basin of Pontian age (c. 5Ma). Fault plane solutions for the main 1969 Banja Luka earthquake (ML 6.4) and its largest foreshock (ML 6.0) indicate reverse faulting along ESE–WNW-striking nodal planes and generally N–S trending pressure axes. The spatial distribution of epicentres and focal depths, analyses of the macroseismic field and fault-plane solutions for several smaller events suggest on-going shortening in the internal Dinarides. Seismic deformation of the upper crust is also associated with strike-slip faults, likely related to the NE–SW trending, sinistral Banja Luka fault. Possibly, this fault transfers contraction between adjacent segments of the Dinarides thrust system. The study area represents the seismically most active region of the Dinarides apart from the Adriatic Sea coast and the bend zone around Zagreb. We propose that on-going thrusting in the internal Dinarides thrust system takes up a portion of the current Adria–Europe convergence.

Study of Local Seismic Events in Lithuania and Adjacent Areas Using Data from the PASSEQ Experiment

The territory of Lithuania and adjacent areas of the East European Craton have always been considered a region of low seismicity. Two recent earthquakes with magnitudes of more than 5 in the Kaliningrad District (Russian Federation) on 21 September 2004 motivated re-evaluation of the seismic hazard in Lithuania and adjacent territories. A new opportunity to study seismicity in the region is provided by the PASSEQ (Pasive Seismic Experiment) project that aimed to study the lithosphere–asthenosphere structure around the Trans-European Suture Zone. Twenty-six seismic stations of the PASSEQ temporary seismic array were installed in the territory of Lithuania. The stations recorded a number of local and regional seismic events originating from Lithuania and adjacent areas. This data can be used to answer the question of whether there exist seismically active tectonic zones in Lithuania that could be potentially hazardous for critical industrial facilities. Therefore, the aim of this paper is to find any natural tectonic seismic events in Lithuania and to obtain more general view of seismicity in the region. In order to do this, we make a manual review of the continuous data recorded by the PASSEQ seismic stations in Lithuania. From the good quality data, we select and relocate 45 local seismic events using the well-known LocSAT and VELEST location algortithms. In order to discriminate between possible natural events, underwater explosions and on-shore blasts, we analyse spatial distribution of epicenters and temporal distribution of origin times and perform both visual analysis of waveforms and spectral analysis of recordings. We show that the relocated seismic events can be grouped into five clusters (groups) according to their epicenter coordinates and origin and that several seismic events might be of tectonic origin. We also show that several events from the off-shore region in the Baltic Sea (at the coasts of the Kaliningrad District of the Russian Federation) are non-volcanic tremors, although the origin of these tremor-type events is not clear.

REVIEW AND A MODEL OF PRE-SEISMIC ELECTROMAGNETIC EMISSIONS IN TERMS OF FRACTAL ELECTRODYNAMICS

We introduce a new model of the generation of pre-seismic electromagnetic emissions, which explains the observed phenomenology in terms of its geometry and fractal electrodynamics. Accumulated evidence indicates that an earthquake can be viewed as a critical phenomenon culminating in a large event that corresponds to a type of critical point. The principle feature of criticality is the fractal organization in both space and time. Earthquakes display a complex spatio-temporal behavior: in addition to the regularity in the rate of occurrence (e.g. Gutenberg-Richter law, Omori law), the spatial distribution of epicenters is fractal and earthquakes occur on a fractal structure of faults. Thus, the hypothesis that the fault develops as a fractal is reasonable. A mounting body of laboratory evidence suggests that micro-fracturing of rocks are associated with the appearance of spontaneous charge production and transient electromagnetic emissions (EME). The emitting, diffusing and recombination charge accompanying the micro-fracturing, can act as current generated during the crack opening. In this view, an active crack or rupture, can be simulated by a "radiating element." The idea is that a fractal geo-antenna (FGA) can be formed as an array of line elements having a fractal distribution on the ground surface as the critical point is approached. We test this idea in terms of fractal electrodynamics: we argue that the precursory VLF-VHF EM signals associated with recent earthquakes in Greece are governed by characteristics (e.g. scaling laws, temporal evolution of the spectrum content, broad band spectrum region and accelerating emission rate) predicted by fractal electrodynamics.

Earthquakes Along the Passive Margin of Greenland: Evidence for Postglacial Rebound Control

— An intriguing observation in Greenland is a clear spatial correlation between seismicity and deglaciated areas along passive continental margins, a piece of evidence for earthquake triggering due to postglacial rebound. Another piece of evidence for induced seismicity due to deglaciation derives from earthquake source mechanisms. Sparse, low magnitude seismicity has made it difficult to determine focal mechanisms from Greenland earthquakes. On the basis of two normal faulting events along deglaciated margins and from the spatial distribution of epicenters, earlier investigators suggested that the earthquakes of Greenland are due to postglacial rebound. This interpretation is tested here by using more recent data. Broadband waveforms of teleseismic P waves from the August 10, 1993 (mb= 5.4) and October 14, 1998 (mb= 5.1) earthquakes have been inverted for moment tensors and source parameters. Both mechanisms indicate normal faulting with small strike-slip components: the 1993 event, strike = 348.9°, dip = 41.0°, rake =−56.3°, focal depth = 11 km, seismic moment = 1.03 × 1024 dyne-cm, and Mw= 5.3; the 1998 event, strike = 61.6°, dip = 58.0°, rake =−95.5°, focal depth = 5 km, seismic moment = 5.72 × 1023 dyne-cm, and Mw= 5.1. These and the two prior events support the theory that the shallow part of the lithosphere beneath the deglaciated margins is under horizontal extension. The observed stress field can be explained as flexural stresses due to removal of ice loads and surface loads by glacial erosion. These local extensional stresses are further enhanced by the spreading stress of continental crust and reactivate preexisting faults. Earthquake characteristics observed from Greenland suggest that the dominant seismogenic stresses are from postglacial rebound and spreading of the continental lithosphere.

Modelling of Block-structure Dynamics: Parametric Study for Vrancea

—The dependence of synthetic earthquake catalog obtained by numerical modelling of block-structure dynamics for the Vrancea (Romania) seismoactive region on values of the model parameters is studied. The features of the synthetic seismicity, such as the spatial distribution of epicentres, the level of seismic activity, the relative activity of the different faults, are considered as functions of the directions of motions of the different blocks of the structure. The likelihood of the features of the synthetic and of the real seismicity could be used as criterion for the reconstruction of the direction of the tectonic motions.

Microseismic Monitoring of Jackson Hole, Wyoming 10 July - 5 October, 1979

As part of the Safety of Dams Program for Jackson Lake Dam, the Service operated an array ot five seismograph stations in the vicinity of Jackson Lake Dam for a period of 87 days. Approximately 110 microearthquakes were recorded in the Jackson Hole area and epicenters were determined using HYPO 71 (Lee and Lahr, 1975). Data from stations DCI and TMI are being incorporated into the Service's data set to provide better location accuracy for events west and south of the network; events in the Teton Range and southern Jackson Hole, respectively. The majority of the epicenters are 5-25 miles east of the Teton Range front in the Mt. Leidy Highlands. The spatial distribution of epicenters in this area is apparently random. However, this area is outside the limits of the seismograph array and the apparent randomness may be a result of poor location accuracy. However, similar monitoring carried out previously by the University of Utah, yielded comparable results. Only eight epicenters fall within 1 mile of the surface trace of the Teton fault, a relatively low number of events for such a major youthful structure. Six epicenters were located near the mouth of Arizona Creek where Behrendt and others (1968) have postulated a north-northwest trending branch of the Teton fault from gravity and seismic refraction data. From this study alone no coherent pattern of seismicity can be determined for Jackson Hole.