Map Of Epicenters Research Articles

Якутия

. The paper presents the results of monitoring seismicity in Yakutia in 2013 based on the data from 24 digital seismic stations. A total of 5197 seismic events with Кp=6–15 are detected. A map of earthquake epicenters is compiled showing their distribution in different areas. Two major clusters of seismic events are recognized. The first one corresponds to the Arctic-Asian seismic belt (AASB) extending across the Laptev Sea shelf and the north eastern Asian continent towards the Sea of Okhotsk. The second Baikal–Stanovoy belt in the south of the region is traced from Lake Baikal through the Stanovoy Highlands and the Stanovoy Ridge to the Sea of Okhotsk. In South Yakutia, the Olekma–Stanovoy zone (OSZ), which makes the eastern part of the belt, is considered. Both belts form boundaries of major lithospheric plates. The first belt separates the Eurasian and North American plates, while the other divides the Eurasian plate from the Amurian one. The minimum seismic level is recorded within the OCZ, with no more than 0.04 % of the total seismic energy re-leased during 2013. The maximum seismicity is noted in the AASB with released energy making up 99.9 % of the total amount. That abrupt change in seismicity is due to the occurrence here of three strong earth-quakes, Ulakhan-Chistay, Ilin-Tas (Abyi), and Tas-Khayakhtakh with the intensities VII-IX in the epicenters (MS=4.9–6.9). The epicentral zone of the Tas-Khayakhtakh event (MS=4.9) that occurred on May, 2013 is considered in more detail. The motion in the source of this event indicate thrusting along the Dogdo fault. All the shakes took place within the Chersky Range, in the zone of influence of major faults of the Kolyma–Indigirka system (Ulakhan, Dogdo, Ilin–Tas) under conditions of NE compression (regime of interplate collision and transpression ). Seismotectonic relations, macroseismic data, and earthquake focal mechanism pa-rameters are discussed.

BELARUS

The annual review of seismicity in the territory of Belarus based on the data of two analogs and eighteen digital stations is presented. Forty-three events with Кd=4.6–8.2 were recorded. These were attributed to the southern part of the territory, which includes the Soligorsk mining area. The map of epicenters of all the events and the table showing their distribution by months are presented. The N(K) function for 2013 was compared with those for 1983–2012. The amount of seismic energy released in 2013 is 1.89 times higher than in 2012 and 5.13 times lower than its average value for the previous 30 years. The distribution of the events according to their energy classes and total seismic energy by months in 2013 as well as for the period of 31 years from 1983 till 2013 was provided. The time history, time of day, and day of week distributions of seismicity recorded in 2013 are presented.

AZERBAIJAN

In 2013, four digital stations («Horadiz», «Agdam», «Beylagan», «Yardimli») were opened. The complete network consisted of 35 digital stations. The network of analog stations continued to operate unchanged. In 2013, the set of parameters for estimating the earthquake size decreased – determining the magnitudes MPVA and the energy classes КР was stopped. Only the local magnitude ML Азр is measured and then recalculated into energy class КР. The seismicity of the territory of Azerbaijan is analyzed. Maps of epicenters of earth-quakes are given. The total number of earthquakes in 2013 was 5248 with ML Азр>0.1, of which only 165 with ML Азр3.0 are published in the Yearbook. A decrease in the seismic activity of the studied territory was noted. Powerful seismic activity, observed in 2012, was replaced in 2013 by a decrease in seismicity to the background level. The most significant seismic event on the territory of the Republic was the April 18 earth-quake with ML Азр=5.3 with macroseismic effect I0=4.

The Problem of the Existence of a Strike-Slip Fault in the Arctic Ocean between Lomonosov Submarine Ridge and the Adjacent Shelf

The junction zone between Lomonosov submarine ridge and the shelf of the East Siberian Sea was studied. The aim was to prove the absence of a strike-slip fault in the junction zone between Lomonosov Ridge and the East Siberian shelf. The problem of the existence of a fault zone in the region where the Lomonosov Ridge joins the East Siberian shelf is still currently debateable. The geological and geophysical data used to solve it are insufficient. To remove this ambiguity, seismological data obtained in neighboring areas were used. An analysis of the map of earthquake epicenters in the region showed that, if the fault zone mentioned existed, present-day intraplate seismic activity would certainly be observed within its limits. The absence of seismicity in the junction zone between Lomonosov Ridge and the adjacent shelf clearly indicates the genetic unity of these structures.

Seismicity of the Arctic in the Early Twentieth Century: Relocation of the 1904–1920 Earthquakes

Abstract The parameters of earthquake hypocenters in the Arctic at the beginning of the twentieth century, published by researchers in the first half of the twentieth century, are still used today for building maps of epicenters of instrumental earthquakes. However, they are based on bulletins that did not use data from all seismic stations operating during that period, and on approximate ideas about the propagation of seismic waves in the Earth. We relocated earthquakes recorded within the Arctic region beginning from the early twentieth century with a view to creating a relocated catalog. For the relocation, we collected all available seismic bulletins from the global network using data acquired for the International Seismological Centre–Global Earthquake Model (ISC-GEM) catalog, the EuroSeismos project, the Geophysical Survey of the Russian Academy of Sciences, and the Russian State Library. The relocation was performed using a modified method of generalized beamforming and the ak135 velocity model. The relocation procedure was applied to 18 of 25 earthquakes in the Arctic region. The new coordinates of some earthquakes turned out to be significantly different from those that were determined previously. As a result, this may have a significant impact on the final seismic hazard assessment of the territory of the Severnaya Zemlya and Franz Josef Land archipelagoes, which are characterized by weak seismicity. Most of the relocated earthquake epicenters are confined to major seismic zones in the Arctic, namely, mid-ocean ridges, the Svalbard Archipelago, and the Laptev Sea shelf. One earthquake, that of 14 October 1914 with magnitude Mw(ISC-GEM)=6.6, occurred in the shelf of the Barents Sea in the “continent–ocean” transition zone near the Franz Victoria graben.

Seismic Events in 2014–2016 around the Karelian Isthmus and Their Nature

For the first time in aseismic Leningrad oblast, the local St. Petersburg seismic network recorded 32 compactly localized seismic events with a unique wave pattern and magnitudes МL = –0.6 to +2.1. The nature of the events has been studied, and spectrograms and cluster analysis are used to show the difference between the records of these events and blasts at the Vyborg station. The source parameters and focal mechanism of thrust-strike movement along a possible northwest-trending fault plane were determined, which proves the tectonic origin of the events. Synthetic seismograms of the strongest event on December 18, 2016, at 00:20 have been constructed, the shapes of which correspond to the position of the source at a depth of 2 km. A map of earthquake epicenters has been compiled, and a 4-km-long NS-trending seismogenic zone has been identified as a fault that bounds the Vyborg rapakivi intrusion from the east, and possibly a new rupture that has occurred in near the long- and intensely functioning Erkilja quarry. The regional earthquakes that took place in the historical and instrumental periods of observations have been described. A database of blasts from known quarries has been created. The velocity model has been refined.

Seismicity of the Central Kuril Islands before and after the catastrophic M = 8.3 (November 15, 2006) and M = 8.1 (January 13, 2007) earthquakes

The data on foreshocks and aftershocks of the strongest earthquakes occurred in the area of Kuril island arc on November 15, 2006 (Mw = 8.3) and January 13, 2007 (Mw = 8.1) are compared. In 2006, two months before the catastrophic earthquake in November, the detailed seismological investigations were carried out with the use of bottom stations in the area of seismic gap in the Central Kuril arc. The maps of epicenters and vertical cross sections for the equal time intervals are compared. The clear difference between distributions of hypocenters in the periods of foreshocks and aftershocks is revealed. Earthquakes were not distributed within the limits of the seismoactive block in the Kuril arc during the foreshocks period; instead, boundaries of seismoactive zone abruptly narrowed and hypocenters concentrated largely within the Benioff zone.

Shallow-focus seismicity and tectonic structure of the Sea of Japan

The analysis of the available seismological data on the Sea of Japan region made it possible to prepare the first complete unified catalog of earthquakes with M ⩾ 3.0 and h ⩽ 60 km for the period of 1975–2010. Four maps of epicenters for different depth intervals (0–10, 11–20, 21–30, and 31–60 km) and three sublatitudinal sections 1° wide are constructed. The analysis includes the structural features and the probable tectonic nature of the seismoactive zone along the underwater margin or borderland of the Japan-Sakhalin island arc: the regional or, more exactly, megaduplex of compression faults determined by the crust sliding in the back part of the frontal deep-seated thrust. The crustal seismicity in the southeastern margin of the Korean Peninsula (the Sino-Korean Shield) is likely related to the Tsushima and Ullyndo faults. It is assumed that it may provoke block, potentially thsunamigenic landslides in the southern and eastern cirques of the Ullyndo Basin incised into the underwater delta of the Huanghe River.

No geologic evidence that seismicity causes fault leakage that would render large-scale carbon capture and storage unsuccessful

In a recent Perspective (1), Zoback and Gorelick argued that carbon capture and storage (CCS) is likely not a viable strategy for reducing CO2 emissions to the atmosphere. They argued that maps of earthquake epicenters portray earthquakes occurring almost everywhere, suggesting that Earth’s crust is near a critical state, so that increments in fluid pressure from injecting CO2 at 1 to 3 km depth will likely trigger earthquakes within the reservoir and caprock that would be expected to result in leakage of CO2 from the reservoirs to the surface.

The possibility of a tsunami on Lake Baikal

Based on the general physical nature of tsunami generation, it is established that it is an attribute of seismically hazardous areas and regions adjacent to large water reservoirs and is threatening to the popula� tion and infrastructure of the coastal zones. The main preconditions and possibilities for the occurrence of tsunami on Lake Baikal are considered: the information on earthquakes in the Baikal hollow during the instrumental-historical period (1724-2011) is generalized in the map of epicenters of shocks of magnitude M ≥ 5 and histograms of the distribution of numbers of shocks with respect to magnitude. It is shown that the tsunami waves start forming on Baikal if the earthquake magnitude M is ≈5, but since a system of tsunami monitoring on Baikal is absent, it can be observed only during the strongest earthquakes of M > 7. The cata� strophic Tsagan earthquake (1861, M ≈ 7.5) is given as an example. It happened near the eastern coast of Lake Baikal and caused a tsunami with people's deaths.

Relations of geodynamic processes, tectonic stresses and strong earthquakes on the Middle Kuril from 2006 through 2009 with eruption of the Sarychev Peak Volcano

It is suggested that the eruption of the Sarycheva Peak volcano on 11 June 2009 may have been related to strong earthquakes which occurred in the Middle Kuril Islands from 2006 through 2009 (Figure 1), geodynamic processes (such as tectonic activation, subduction, and friction of contacting blocks), tectonic stresses, melting of rocks, rising of the melting substance, gases and fluids. The publication discusses the earthquake hypocenters profile along the Kuril Islands (Figure 2), the seismogeological depth profile of volcanoes of the Kuril Islands that was published by T.K. Zlobin (Figure 3), and positions of the magmatic chamber and the seismogenic zone of the SenHelens volcano from the publication by S. Carey (Figure 4). The map of earthquake epicenters for the Middle Kuril Islands is constructed on the basis of the NEIC catalogue (Figure 5). A corresponding depth profile showing earthquake hypocenters is constructed (Figure 6). An aseismic area is detected underneath the Matua Island (Sarychev Peak volcano) ; it is almost 30 km wide and about 200 km thick. In the Middle Kuril Islands, magma lifting and eruption were facilitated by stretching of the lithosphere (Figure 7), occurrence and activation of breaks, fractures and faults due to earthquakes which occurred from 2006 though 2009, and lifting of gas and fluids (Figure 8). The eruption was possible by explosion upon instant injection of fluids into the porous space due to considerable shear stresses, which occurred after the earthquakes, and the reaction of dehydration. It can also result from supply of volcanic gases and fluids, according to the vacuumexplosion fluid dynamics model.

The mechanics of a magma chamber-fault system in trans-tension with application to Coso

The mechanical interaction between an elliptically shaped magma chamber and a fault subject to transtension is investigated with particular reference to the Coso geothermal field. The geologic setting of the Coso field is interpreted as a releasing bend step-over structure formed by the Airport Lake and Owens Valley dextral strike-slip fault system. The role of the Coso volcano-magmatic center in the development of the “over-step” structure is examined by treating the magma chamber as a liquid inclusion in a viscoelastic crust containing a fault (Airport Lake). The problem is numerically solved using a 2D viscoelastic finite element model with thermally activated viscosity to account for thermal weakening of the rock. The temperature distribution around the magma body is calculated based on a 3D steady-state approach and using the mesh-less numerical method. The fault is modeled as a frictionless contact. The simulated distributions of stress and strain around the inclusion display a rotation caused by the shearing component of the applied transtension. The results indicate that the fault tends to overstep the chamber in a geometric pattern similar to a step-over. There is good correspondence between the computed distributions of the maximum shear stress in the vicinity of the magma chamber and the map of earthquake epicenters at a depth of 7–10 km in Coso.

Maps of epicentral distribution in 2003

For showing the epicentral distribution in and near China as well as all over the world, two epicentral maps for the earthquakes occurred last year are published annually in the 6-th issue each year. Figures 1 and 2 represent the epicentral distributions in and near China and all over the world in 2003, respectively.……

Location Robustness of Earthquakes in Sichuan Province, China

The Sichuan Province in China is located in the middle section of a large north-south seismicity belt. The Xianshuihe Fault striking northwest-southeast, the Longmenshan east fault striking north-south, and the Anninghe Fault striking north-south together form a “Y” shape. Sichuan is located in the east margin of the Qinghai-Tibet crustal block. More than 8,000 earthquakes with magnitude 0.0 occur in Sichuan every year, and 2,000 of these can be located (Han and Lu, 2001). Since 26 B.C., 240 strong earthquakes have occurred in Sichuan with magnitude ML ≥ 5.0. Fifty of these events had ML 6.0-6.9, and 19 of them had ML 7.0-7.9. These events are distributed mainly along several faults and form seismic zones such as the Xianshuihe, the Songpan-Longmenshan, the Anninghe-Zemuhe, the Jinshajiang, and the Mingshan-Mabian-Zhaotong seismic zones (Han and Lu, 2001). A map of earthquake epicenters in Sichuan Province for events with magnitude greater than 2.5 during the period 1970 through 30 April 2003 is shown in Figure 1. In general, seismic epicenters in Sichuan Province show a diffuse spatial pattern rather than sharp linear alignment. The complex tectonic structure of the region, with crustal thickness varying between about 40 and 65 km (Ren et al. , 1987; Beghoul et al. , 1993; Vincent, 2000) and great sediment thickness over the Sichuan basin, creates a three-dimensional seismic velocity structure that affects the calculated locations. In this study we selected from a group of 1D velocity models the one that best fit the travel times of three ground-truth (GT) events from Sichuan, China. Based on this 1D velocity model, a set of station corrections for 106 stations in Sichuan area was generated. For the purpose of locating earthquakes quickly and within the desired accuracy, we modified the software programs Hypoinverse (Hypo) …

Study of the epicentral trends and depth sections for aftershocks of the 26th january 2001, Bhuj earthquake in Western India

The Geological Survey of India (GSI) established a twelve-station temporary microearthquake (MEQ) network to monitor the aftershocks in the epicenter area of the Bhuj earthquake (M w7.5) of 26th January 2001. The main shock occurred in the Kutch rift basin with the epicenter to the north of Bhachao village, at an estimated depth of 25 km (IMD). About 3000 aftershocks (M d ≥ 1.0), were recorded by the GSI network over a monitoring period of about two and half months from 29th January 2001 to 15th April 2001. About 800 aftershocks (M d ≥ 2.0) are located in this study. The epicenters are clustered in an area 60 km × 30 km, between 23.3‡N and 23.6‡N and 70‡E and 70.6‡E. The main shock epicenter is also located within this zone.Two major aftershock trends are observed; one in the NE direction and other in the NW direction. Out of these two trends, the NE trend was more pronounced with depth. The major NE-SW trend is parallel to the Anjar-Rapar lineament. The other trend along NW-SE is parallel to the Bhachao lineament. The aftershocks at a shallower depth (<10km) are aligned only along the NW-SE direction. The depth slice at 10 km to 20 km shows both the NE-SW trend and the NW-SE trend. At greater depth (20 km–38 km) the NE-SW trend becomes more predominant. This observation suggests that the major rupture of the main shock took place at a depth level more than 20 km; it propagated along the NE-SW direction, and a conjugate rupture followed the NW-SE direction.A N-S depth section of the aftershocks shows that some aftershocks are clustered at shallower depth ≤ 10 km, but intense activity is observed at 15–38 km depth. There is almost an aseismic layer at 10–15 km depth. The activity is sparse below 38 km. The estimated depth of the main shock at 25 km is consistent with the cluster of maximum number of the aftershocks at 20–38 km. A NW-SE depth section of the aftershocks, perpendicular to the major NE-SW trend, indicates a SE dipping plane and a NE-SW depth section across the NW-SE trend shows a SW dipping plane.The epicentral map of the stronger aftershocksM ≥ 4.0 shows a prominent NE trend. Stronger aftershocks have followed the major rupture trend of the main shock. The depth section of these stronger aftershocks reveals that it occurred in the depth range of 20 to 38 km, and corroborates with a south dipping seismogenic plane.

Map of epicentre distribution for 2000

For showing the epicentral distribution in and near China as well as all over the world, two epicentral maps for the earthquakes occurred last year are published annually in the 6-th issue each year. Figures 1 and 2 represent the epicentral distribution in and near China and all over the world in 2000, respectively.

Spatial distribution of scalar seismic moment release in Italy (1983-1996): seismotectonic implications for the Apennines

We analyzed the distribution of seismic moment in Italy, computed from instrumental seismicity recorded by the Italian National Seismic Network in the past 14 years, to map the areas where seismic deformation processes have been active in this time interval. Seismic moment is the most suitable parameter to quantify earthquake size. It is related to the geometric characteristics of faults, to seismic energy and it is a quantity that can be summed and represented in its cumulative value. The maps of seismic moment distribution display more information than epicentral maps, better showing actively deforming regions. They provide further and original evidence for the existence, within the Apenninic belt, of two regions (north and south) characterized by different seismic energy release. The seismic moment is almost continuously and homogeneously distributed all along the belt in the Northern Apennines, whereas in the Southern Apennines it is concentrated in the zones recently activated by mainshock-aftershock seismic sequences. Seismic deformation takes place in a 30 km narrow belt along the Apennines, while in the transition zone between the Northern and Southern Apennines this belt is about 100 km wide. Comparing instrumental seismic moment release with the areas struck by the largest historical earthquakes which have occurred in the past six centuries, we qualitatively extended back to the past the information on where the seismic deformation occurs. In the Southern Apennines background energy release from instrumental seismicity is very low in the several areas hit by large historical earthquakes, suggesting that these seismogenic zones are currently quiescent.

Distribution map of epicenters in 1992

Distribution map of epicenters in 1992

Aftershock sequences of intermediate‐depth earthquakes in the Pamir‐Hindu Kush Seismic Zone

We examine the space‐time seismicity patterns associated with the 40 largest (M≥5.6), intermediate‐depth earthquakes that occurred in the Pamir‐Hindu Kush zone between 1962 and 1984 to determine if any of these events were followed by aftershock sequences. To address this issue we examined data from the Soviet Central Asia regional earthquake catalog with two complementary techniques: (1) a subjective technique based on inspection of epicentral maps, and (2) a quantitative method which assumed that the background seismicity was a Poisson process and which detected aftershocks as significant departures, as quantified by the Poisson model, from background rates. Of the 40 events we examined, only three were identified by both methods as having clearly defined aftershock sequences. These three events are also remarkably similar in several other ways: (1) they occurred at almost the same point in space, (2) they have indistinguishable focal mechanisms, (3) they have similar magnitudes, and (4) they define two nearly equal time intervals (9.37 and 9.41 years). No other events in the Pamir‐Hindu Kush zone exhibit comparable aftershock behavior. Six other events show rate anomalies, but the subjective method rated them negative or at least ambiguous. Four of these six we argue are caused by coincidental or man‐made rate increases at the time of the mainshock. The remaining two are noteworthy because they are the two largest events to have occurred beneath the central Pamir. Each of these events shows a small, short burst of seismicity around the time period of the largest event in the sequence. We suggest two alternative hypotheses to explain our observations: (1) more events may have aftershock sequences, but the aftershocks are too small to be detected; or (2) the three events that had clear aftershocks are unique, and trigger a burst of aftershocks only because they have a special relationship to the the most active nest of activity in the Hindu Kush zone.

Accuracy of historical earthquake locations in Britain

AbstractIf historical earthquake data are to be used in studies of regional seismotectonics, it is essential to include information on likely locational uncertainty. Contributory factors include both geophysical parameters and the social environment of the event. A reconstruction of how a recent earthquake might have appeared had it occurred 300 years ago is used to demonstrate the effects of documentary survival. Limits of uncertainty are estimated for two historical earthquakes (7 October 1690 and 28 November 1880) and shown to be large. It is recommended that such events should be shown on epicentral maps as areas rather than points.