scholarly journals Geodynamics of the Talish region according to earthquake source mechanisms and GPS-stations

2020 ◽  
Author(s):  
С.Э. Казымова ◽  
И.Э. Казымов
Keyword(s):  
Normal Faults ◽  
Tectonic Structure ◽  
Strong Earthquakes ◽  
Earthquake Sources ◽  
Source Mechanisms ◽  
Westerly Direction ◽  
Gps Observation ◽  
Using Data ◽  
Main Influence ◽  
Gps Observations

В статье представлено описание тектонического строения иссле- дуемого региона, а также проанализирована геодинамика Талышского региона по данным механизмов очагов землетрясений. Целью работы являлось определить скорости современных горизонтальных сме- щений отдельных тектонических блоков Талышского региона и проанализировать влияние их на сильные землетрясения, произошедшие за 2016 и 2019 гг. Методы исследования. На основе метода полярности первых вступлений продольных волн были проанализированы механизмы очагов землетрясений. Анализ показал, что в исследуемом регионе в основном преобладает тип подвижки – взброс и сдвиг. Углы паде- ния для подвижек разных типов превышают 45°, что свидетельствует о достаточно крутом погружении зон разломов. Это согласуется с тем, что в исследуемой зоне большинство поперечных разломов имеет углы падения сместителей 50‑90°, то есть углы, достаточно близкие к вертикали. Основное влияние на сейсмическую активность оказывают Талышский, Предталышский, Ярдымоинский и Астаринские разло- мы. Результаты исследования. На основе полученных результатов была построена схематическая карта ориентации осей сжатия и растяжений исследуемых сильных землетрясений. На основе катакластиче- ского анализа механизмов очагов землетрясений c ml>3,0. Установлено, что большая часть исследуемой территории подвержена сжатию, сдвиги отмечены в районе Лерика и Ярдымлы. Для Талышского региона установлены три основных типа подвижек: взбросы (36 %), сдвиги (34 %) и сбросы (30 %). Анализ ско- ростей горизонтальных движений по данным GPS-наблюдений показал движение поверхности земной коры в С-СВ направлении относительно Евразии. Отмечено уменьшение скорости в пунктах наблюдений PQLG, XNGG, ZKTG, ATGG, IMLG и GBLG, расположенных перпендикулярно к Главному Кавказкому Над- вигу. Пункты GPS-наблюдений, расположенные вдоль ГКН, показывают уменьшение скорости в западном направлении. С-СВ движение земной поверхности интерпретируется как одна из причин накопления на- пряжений на этом надвиге. In addition, the article provides a description of the tectonic structure of the region under study, and also analyzes the geodynamics of the Talish region using data from the mechanisms of earthquake sources. Aim of the work was to determine the velocities of modern horizontal displacements of individual tectonic blocks of the Talish region and to analyze their influence on strong earthquakes that occurred in 2016 and 2019yy. Methods. Based on the method of polarity of the first arrivals of longitudinal waves, the mechanisms of earthquake sources were analyzed. The analysis showed that in the studied region the type of movement predominates – reverse faults and strike-slips. The angles of incidence for motions of various types exceed 45°, which indicates a rather steep immersion of fault zones. This is consistent with the fact that in the studied zone the majority of transverse faults have angles of incidence of 50‑90°, that is, angles quite close to the vertical. The main influence on seismic activity is exerted by the Talish, Predtalish, Yardimli and Astara faults. Results. Based on the results obtained, a schematic map of the orientation of the compression and extension axes of the studied strong earthquakes was constructed. On the basis of a cataclastic analysis of the mechanisms of earthquake sources with ml> 3.0, it was established that most of the study area is subject to compression, strike-slip faults were noted in the Lerik and Yardimla regions. For the Talish region, three main types of shifts are established: reverse faults (36 %), strike-slips (34 %) and normal faults (30 %). An analysis of horizontal velocities according to GPS observations showed the movement of the surface of the earth’s crust in the northwest direction relative to Eurasia. A decrease in speed was noted at the observation points PQLG, XNGG, ZKTG, ATGG, IMLG and GBLG located perpendicular to the Main Caucasian Thrust. GPS observation points located along the Main Caucasian Thrust show a decrease in speed in a westerly direction. C-NE motion of the earth’s surface is interpreted as one of the reasons for the accumulation of stresses on this thrust

scholarly journals Characteristics of local earthquake seismograms of varying dislocation sources in a stratified upper crust and modeling for P and S velocity structure: comparison with observations in the Koyna-Warna region, India

2016 ◽  
Vol 58 (6) ◽  
Author(s):  
V. G. Krishna
Keyword(s):  
Velocity Structure ◽  
Source Parameters ◽  
Velocity Model ◽  
Strike Slip ◽  
Synthetic Seismograms ◽  
Structure Comparison ◽  
Earthquake Sources ◽  
Crustal Velocity ◽  
Source Mechanisms ◽  
Local Earthquake

<p>Vertical component record sections of local earthquake seismograms from a state-of-the-art Koyna-Warna digital seismograph network are assembled in the reduced time versus epicentral distance frame, similar to those obtained in seismic refraction profiling. The record sections obtained for an average source depth display the processed seismograms from nearly equal source depths with similar source mechanisms and recorded in a narrow azimuth range, illuminating the upper crustal P and S velocity structure in the region. Further, the seismogram characteristics of the local earthquake sources are found to vary significantly for different source mechanisms and the amplitude variations exceed those due to velocity model stratification. In the present study a large number of reflectivity synthetic seismograms are obtained in near offset ranges for a stratified upper crustal model having sharp discontinuities with 7%-10% velocity contrasts. The synthetics are obtained for different source regimes (e.g., strike-slip, normal, reverse) and different sets of source parameters (strike, dip, and rake) within each regime. Seismogram sections with dominantly strike-slip mechanism are found to be clearly favorable in revealing the velocity stratification for both P and S waves. In contrast the seismogram sections for earthquakes of other source mechanisms seem to display the upper crustal P phases poorly with low amplitudes even in presence of sharp discontinuities of high velocity contrasts. The observed seismogram sections illustrated here for the earthquake sources with strike-slip and normal mechanisms from the Koyna-Warna seismic region substantiate these findings. Travel times and reflectivity synthetic seismograms are used for 1-D modeling of the observed virtual source local earthquake seismogram sections and inferring the upper crustal velocity structure in the Koyna-Warna region. Significantly, the inferred upper crustal velocity model in the region reproduces the synthetic seismograms comparable to the observed sections for earthquake sources with differing mechanisms in the Koyna and Warna regions.</p>

scholarly journals Comparison of simultaneous variations of the ionospheric total electron content and geomagnetic field associated with strong earthquakes

2001 ◽  
Vol 1 (1/2) ◽  
pp. 53-59 ◽  
Author(s):  
Sh. Naaman ◽  
L. S. Alperovich ◽  
Sh. Wdowinski ◽  
M. Hayakawa ◽  
E. Calais
Keyword(s):  
Total Electron Content ◽  
Vertical Displacement ◽  
Temporal Variations ◽  
Electron Content ◽  
Geomagnetic Disturbances ◽  
Total Electron ◽  
Strong Earthquakes ◽  
Ionospheric Total Electron Content ◽  
Geomagnetic Observations ◽  
Gps Observations

Abstract. In this paper, perturbations of the ionospheric Total Electron Content (TEC) are compared with geomagnetic oscillations. Comparison is made for a few selected periods, some during earthquakes in California and Japan and others at quiet periods in Israel and California. Anomalies in TEC were extracted using Global Positioning System (GPS) observations collected by GIL (GPS in Israel) and the California permanent GPS networks. Geomagnetic data were collected in some regions where geomagnetic observatories and the GPS network overlaps. Sensitivity of the GPS method and basic wave characteristics of the ionospheric TEC perturbations are discussed. We study temporal variations of ionospheric TEC structures with highest reasonable spatial resolution around 50 km. Our results show no detectable TEC disturbances caused by right-lateral strike-slip earthquakes with minor vertical displacement. However, geomagnetic observations obtained at two observatories located in the epicenter zone of a strong dip-slip earthquake (Kyuchu, M = 6.2, 26 March 1997) revealed geomagnetic disturbances occurred 6–7 h before the earthquake.

scholarly journals The Paleogene Tectonostratigraphy Of Northern Part Masalima Trench Basin

2016 ◽  
Vol 1 (1) ◽  
pp. 7
Author(s):  
Luhut Pardamean Siringoringo ◽  
Dardji Noeradi
Keyword(s):  
Depositional Environment ◽  
Middle Eocene ◽  
Normal Faults ◽  
Tectonic Structure ◽  
Shallow Marine ◽  
Early Oligocene ◽  
Basin Formation ◽  
Java Sea ◽  
Seismic Sections ◽  
Well Data

Northern part of Masalima Trench Basin is located in the southern part of the Strait of Makassar, which includes Masalima Trough and Massalima High. The area of research is an extension of the South Makassar Basin which extends from South Makassar Basin to the Northeast part of Java Sea. Subsurface data are used such as 2D seismic sections (21 lines) and data drilling wells (2 wells) to understand the tectonic structure in the basin formation and understand the stratigraphic order of basin. Based on well data can be known that Northern part Masalima Trench Basin is aborted rift because marked by post rift phase. Northern part Masalima Trench Basin was formed by normal faults which have trend northeast-southwest with  pre rift, early syn rift, late syn rift, and post rift sediment geometry. Early syn rift sediment was Middle Eocene, late syn rift sediment was Middle Eocene till Early Oligocene and post rift sediment was Early Oligocene till Early Miocene. The Depositional environment of early syn rift phase such as beach, shallow marine, and land. The Depositional environment of late syn rift phase such as beach till deep marine, and the depositional environment of post rift is deep marine.

scholarly journals ABOUT SOIL SEISMIC VIBRATIONS SPECTRA IN EARTHQUAKE NEAR ZONE

2015 ◽  
Author(s):  
Э.Г. Геодакян ◽  
С.М. Оганесян ◽  
С.Н. Саргсян ◽  
Дж.К. Карапетян
Keyword(s):  
Earthquake Source ◽  
Dynamic Parameters ◽  
Seismic Zoning ◽  
Strong Earthquakes ◽  
Earthquake Sources ◽  
Instrumental Observations ◽  
Near Zone ◽  
Seismic Vibrations ◽  
Source Physics ◽  
Seismic Impacts

Изучение спектральных и динамических параметров очагов землетрясений по данным инженерных макросейсмических и инструментальных наблюдений необходимо для решения многих задач фундамен- тальной и прикладной сейсмологии. Это задачи физики очага, процессов подготовки сильных землетря- сений, задачи сейсмического районирования, микрорайонирования, расчета сейсмических воздействий, геофизической защиты территории и т. д. Study of spectral and dynamic parameters of earthquake sources with the help of the data of engineering macroseismic and instrumental observations is necessary for many fundamental and applied seismology problems solving. These are the problems of earthquake source physics, processes of strong earthquakes origination, problems of seismic zoning, microzonation, seismic impacts calculation, geophysical protection of territory etc.

scholarly journals THE APRIL 2007 SWARM IN TRICHONIS LAKE USING DATA FROM A MICROSEISMIC NETWORK

2017 ◽  
Vol 43 (4) ◽  
pp. 2183
Author(s):  
E. Sokos ◽  
V.E. Pikoulis ◽  
E.Z. Psarakis ◽  
A. Lois
Keyword(s):  
Aftershock Sequence ◽  
Lake Area ◽  
Regional Networks ◽  
Strong Earthquakes ◽  
Waveform Cross Correlation ◽  
Short Period ◽  
Using Data ◽  
Almost All ◽  
The University ◽  
Space Time Evolution

A series of strong earthquakes took place at the Trichonis lake area, during April 2007. Three events, with M~5.0 occurred within one day, causing damages to almost all nearby villages and especially at the small town of Thermo. The sequence lasted for more than one month with small to moderate size events. It was recorded by regional networks and results related to its time and space evolution have already been published. Just after the major events a microseismic network was deployed in the area, by the University of Patras, Seismology Laboratory. Eight stations were installed, with short period, three component sensors and portable digital recorders. The network was in operation for a period of one month and a lot of events were recorded by enough stations to provide a reliable location. We present here the analysis of these data using modern methodologies like waveform cross-correlation techniques and further relocation of the events using waveform based differential time. The results partially support the findings of the regional networks, as regards the gross characteristics of the aftershock sequence, but provide an enhanced description of it. The space time evolution of the aftershock sequence reveals the activation of more than one fault in the area and suggests the connection of the sequence with an unmapped fault.

Detection of possible seismic station phase reversals using parametric data from seismological bulletins

2021 ◽  
Author(s):  
Konstantinos Lentas
Keyword(s):  
Goodness Of Fit ◽  
Seismic Station ◽  
Waveform Data ◽  
Seismic Stations ◽  
Velocity Models ◽  
Parametric Data ◽  
Source Mechanisms ◽  
First Motion ◽  
Earthquake Mechanism ◽  
Using Data

&lt;p&gt;A simple and fast technique to detect systematic changes in the performance of seismic stations by using parametric data is being presented. The methodology is based on a simple principal, notably, quantifying the goodness of fit of first motion manually picked polarities from seismological bulletins versus available earthquake mechanism solutions over time. The probability of the reporting polarity data fitting (and not fitting) source mechanisms is quantified by calculating the probability distribution of several Bernoulli trials over a randomly perturbed set of hypocentres and velocity models for each earthquake mechanism - station polarity combination. The method was applied to the registered seismic stations in the bulletin of the International Seismological Centre (ISC) after grouping each polarity pick by reporting agency, using data from the past two decades. The overall agreement of first motion polarities against source mechanisms is found to be good with a few cases of seismic stations showing indications of systematic phase reversals over certain time periods. Specifically, results were obtained for 50% of the registered stations at the ISC, and from these stations 70% show reliable operation during the operational time period under investigation, with only 3% showing the opposite, and 7% showing evidence of systematic changes in the quality of the reported first motion polarities. The rest showed great variability over short periods of time, which does not allow one to draw any conclusions. Comparing waveform data with the associated reported polarities revealed a mixture of cases of either questionable picking or true station phase reversals.&lt;/p&gt;

Anomalously deep earthquakes in the March 2018 swarm along the Western Margin of Afar

2020 ◽  
Author(s):  
Alessandro La Rosa ◽  
Cecile Doubre ◽  
Carolina Pagli ◽  
Federico Sani ◽  
Giacomo Corti ◽  
...  
Keyword(s):  
Lower Crust ◽  
Surface Deformation ◽  
Receiver Function ◽  
Velocity Model ◽  
Normal Faults ◽  
Active System ◽  
Western Margin ◽  
Afar Depression ◽  
Crustal Earthquakes ◽  
Using Data

&lt;p&gt;During the evolution of continental rift systems, extension focuses along on-axis magmatic segments while extensional structures along the rift margins seem to progressively become inactive. However, how strain is partitioned between rift axes and rift margins is still poorly understood. The Afar Rift is the locus of extension between Nubia, Arabia and Somalia and is believed to record the latest stages of rifting and incipient continental break-up. The Afar rift axis is bounded at its western margin by a seismically active system of normal faults separating the Afar depression from the Ethiopian Plateau through a series of large bounding faults and marginal grabens. Although most of the extension in Afar is currently accommodated on-axis, several earthquakes with Mw &gt; 5.0 occurred in the past decades on the Western Afar Margin (WAM). Here we analysed the most recent M&lt;sub&gt;w&lt;/sub&gt; 5.2 earthquake on the WAM on 24 March 2018 and the following seismic sequence using data recorded by a temporary seismic network, set up between 2017 and 2018. We located 800 events from the 20 March to the 30 April 2018 using twenty-three local seismic stations and a new velocity model for the WAM based on a new receiver function study. Preliminary results show that seismicity during the 2018 event focused at mid-to-low crustal depths (from ~15 km to ~35 km) along west-dipping fault planes. Shallower upper crustal earthquakes also occurred on west-dipping fault planes.&lt;/p&gt;&lt;p&gt;The hypocentral location of the mainshock has also been investigated using InSAR. We processed four independent interferograms using Sentinel-1 data acquired from a descending track. None of them shows any significant surface deformation, confirming the large depth of the hypocenters. Furthermore, we tested possible ranges of depth by producing a series of forward models assuming fault located at progressively increasing depths and corresponding to a Mw 5.2 earthquake. Our models show that surface deformations are &lt; 1 cm at depths greater than 15 km, in agreement with our hypocentral depth of 18 km for the main shock estimated from seismic data.&amp;#160;&lt;/p&gt;&lt;p&gt;Our seismicity observations of slip along west-dipping faults show that deformation across the WAM is currently accommodated by antithetic faulting, as suggested by structural geology studies. Lower crustal earthquakes might occur in a strong lower crust due to the presence of mafic lower crust and/or be induced by migrating fluids such as magma or CO&lt;sup&gt;2&lt;/sup&gt;.&lt;/p&gt;

scholarly journals Defining a mid-Holocene earthquake through speleoseismological and independent data: implications for the outer Central Apennines (Italy) seismotectonic framework

Solid Earth ◽  
2017 ◽  
Vol 8 (1) ◽  
pp. 161-176 ◽  
Author(s):  
Alessandra Di Domenica ◽  
Alberto Pizzi
Keyword(s):  
Normal Fault ◽  
Transitional Zone ◽  
Quantitative Modeling ◽  
Normal Faults ◽  
Independent Data ◽  
The West ◽  
Central Apennines ◽  
Strong Earthquakes ◽  
Surrounding Areas ◽  
Karst Conduit

Abstract. A speleoseismological study has been conducted in the Cavallone Cave, located in the easternmost carbonate sector of the Central Apennines (Maiella Massif), in a seismically active region interposed between the post-orogenic extensional domain, to the west, and the contractional one, to the east. The occurrence of active silent normal faults, to the west, close to blind thrusts, to the east, raises critical questions about the seismic hazard for this transitional zone. Large collapses of cave ceilings, fractures, broken speleothems with new re-growing stalagmites on their top, preferential orientation of fallen stalagmites and the absence of thin and long concretions have been observed in many portions of the karst conduit. This may indicate that the cave suffered sudden deformation events likely linked to the occurrence of past strong earthquakes. Radiocarbon dating and, above all, the robust correspondence with other coeval on-fault and off-fault geological data collected in surrounding areas outside the cave, provide important constraints for the individuation of a mid-Holocene paleoearthquake around 4.6–4.8 kyr BP. On the basis of the available paleoseismological data, possible seismogenic sources can be identified with the Sulmona normal fault and other active normal fault segments along its southern prosecution, which recorded synchronous strong paleoevents. Although the correlation between speleotectonic observations and quantitative modeling is disputed, studies on possible effects of earthquake on karstic landforms and features, when corroborated by independent data collected outside caves, can provide a useful contribution in discovering past earthquakes.

scholarly journals Active faults of the Kerch’s Peninsula: new results

2019 ◽  
Vol 488 (4) ◽  
pp. 408-412
Author(s):  
А. N. Ovsyuchenko ◽  
R. N. Vakarchuk ◽  
A. M. Korzhenkov ◽  
A. S. Larkov ◽  
А. I. Sysolin ◽  
...  
Keyword(s):  
Seismic Hazard ◽  
Strong Earthquake ◽  
Late Holocene ◽  
Active Fault ◽  
Active Faults ◽  
Fault Zones ◽  
Strong Earthquakes ◽  
Earthquake Sources ◽  
Kerch Peninsula ◽  
Seismotectonic Model

In the paper there are results of a recent study of the active faults in the Kerch Peninsula. There was compiled a Map of Active Faults - sources of the strong earthquakes occurred in Late Holocene. The map is a regional seismotectonic model of strong earthquake sources - detailed basis for a spatial prognosis of the seismic hazard. Results of the study show that the Kerch Peninsula demonstrates signs of the classical morphostructures, and a morphology of the modern peninsula contours is caused by the large active fault zones.

scholarly journals Relocation of clustered earthquakes in the Groningen gas field

2017 ◽  
Vol 96 (5) ◽  
pp. s163-s173 ◽  
Author(s):  
Lisanne Jagt ◽  
Elmer Ruigrok ◽  
Hanneke Paulssen
Keyword(s):  
S Wave ◽  
Gas Field ◽  
Single Station ◽  
Source Mechanisms ◽  
The Difference ◽  
Multiplet Analysis ◽  
Using Data ◽  
Groningen Gas Field ◽  
Master Event ◽  
Improved Accuracy

AbstractPrevious locations of earthquakes induced by depletion of the Groningen gas field were not accurate enough to infer which faults in the reservoir are reactivated. A multiplet analysis is performed to identify clusters of earthquakes that have similar waveforms, representing repeating rupture on the same or nearby faults. The multiplet analysis is based on the cross-correlation of seismograms to assess the degree of similarity. Using data of a single station, six earthquake clusters within the limits of the Groningen field were identified for the period 2010 to mid-2014. Four of these clusters were suitable for a relocation method that is based on the difference in travel time between the P- and the S-wave. Events within a cluster can be relocated relative to a master event with improved accuracy by cross-correlating first arrivals. By choosing master events located with a new dense seismic network, the relocated events likely not only have better relative, but also improved absolute locations. For a few clusters with sufficient signal-to-noise detections, we show that the relocation method is successful in assigning clusters to specific faults at the reservoir level. Overall, about 90% of the events did not show clustering, despite choosing low correlation thresholds of 0.5 and 0.6. This suggests that different faults and/or fault segments with likely varying source mechanisms are active in reservoir sub-regions of a few square kilometres.

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