scholarly journals The recent instrumental seismicity of Syria and its implications

2018 ◽  
Vol 57 (2) ◽  
Author(s):  
Mohamad Khir Abdul-Wahed ◽  
Jamal Asfahani
Keyword(s):  
Seismic Activity ◽  
Current Knowledge ◽  
Active Faults ◽  
Historical Seismicity ◽  
Focal Mechanisms ◽  
Seismic Events ◽  
Earthquake Activity ◽  
Return Periods ◽  
Cluster Type ◽  
Large Earthquakes

This contribution is an attempt to enlarge the current knowledge about the recent instrumental seismicity, recorded during the period 1995- 2012 by the Syrian national seismological network, as well as the seismotectonic settings in Syria. The recent instrumental seismicity has shown that the earthquake activity has produced a little number of low magnitude events. Consequently, it indicates that this activity is actually passing through a relative quiescence in comparison with the historical seismicity. The correlation between the instrumental seismicity and the seismotectonic features was performed by analyzing spatial distributions of seismic events and focal mechanisms of some strongest events. The current results, allow observing many types of the seismic activity as follows: Swarm-type, Cluster- type, and Occasional-type, which could improve the understanding of the behavior of the seismically active faults. The long return periods of large earthquakes (M?5) and the shortness of instrumental seismicity, prevent us to completely characterize the seismic activity and to discover all the active faults in the country.

scholarly journals Recent geodynamics, active faults and earthquake focal mechanisms of the zone of pseudosubduction interaction between the Northern and Southern Caucasus microplates in the southern slope of the Greater Caucasus (Azerbaijan)

2018 ◽  
Vol 9 (4) ◽  
pp. 1099-1126 ◽  
Author(s):  
T. N. Kangarli ◽  
F. A. Kadirov ◽  
G. J. Yetirmishli ◽  
F. A. Aliyev ◽  
S. E. Kazimova ◽  
...  
Keyword(s):  
Seismic Activity ◽  
Active Faults ◽  
Accretionary Prism ◽  
Focal Mechanisms ◽  
Northern Caucasus ◽  
Seismic Events ◽  
Southern Slope ◽  
Compression Process ◽  
Greater Caucasus ◽  
Southern Caucasus

Our study was focused on the active tectonics of the southern slope of the Greater Caucasus within Azerbaijan. The study area is the zone of under-thrusting (pseudosubduction) interaction between Southern and Northern Caucasus continental microplates, which caused the tectonic stratification of the Alpine formations into various allochthonous and parauthochthonous thrust slices of southern vergency between the Middle Bajocian and Quaternary periods. These slices are grouped into the nappe complexes that form the modern structure of the trough in the study area. The large linearly stretched tectonic units (megazones) correspond to the axis of the Alpine marginal sea basin, the consolidated crust of which is subjected to destruction and thinning. The trough’s Alpine cover was compressed in the underthrust zone and pushed southwards. As a result, an accretionary prism formed allochthonously overlapping the northern side of the Southern Caucasus microplate by the system of gently dipping overthrusts. During the continental stage of Alpine tectogenesis (starting from the end of Miocene), intensive lateral compression process was caused by intrusion of the frontal wedge of the Arabian indenter into the buffer structures of the southern frame of Eurasia. This is evidenced by the GPS monitoring data on modern geodynamic activity, which demonstrates the Southern Caucasus block’s intensive (up to 29 mm/year) intrusion in the northern rhumbs as compared to the relative stability of the Northern Caucasus microplate (0–6 mm/year). This, in turn, is a reflection of the ongoing pseudosubduction regime (continental subduction or S-subduction) at the band of collision junction of these microplates. It is suggested that this process caused historically observed seismic activity in the study area, wherein the earthquakes occurred mainly in the southern slope’s accretionary prism area and the adjacent strip of the Southern Caucasus microplate. In this article, we analyze and correlate the whole range of seismic events that occurred in the study area until 2017 and the focal mechanisms of the recently recorded earthquakes (2012–2016). It is established that earthquake foci are confined either to the intersection nodes of variously trending ruptures with the faults of different directions or to the planes of deep tectonic ruptures and lateral displacements along the unstable contacts between the material complexes with different competence. The focal mechanisms of seismic events reveal various, mostly near-vertical, planes of normal and strike-slip faults. However, the earthquake foci are generally confined to the intersection nodes between the Caucasus and anti-Caucasus-striking rupture dislocations. The results of our studies are interesting in terms of their real-time application for drawing a regional summary of causes for both geodynamic and seismic activity of the Greater Caucasus system and the adjacent areas of Alpine-Himalayan fold belt.

scholarly journals Glacial rumblings from Jakobshavn ice stream, Greenland

2009 ◽  
Vol 55 (191) ◽  
pp. 389-399 ◽  
Author(s):  
J.A. Rial ◽  
C. Tang ◽  
K. Steffen
Keyword(s):  
Seismic Activity ◽  
Seismic Energy ◽  
Seismic Events ◽  
Earthquake Activity ◽  
Mass Wasting ◽  
Close Inspection ◽  
Seismic Amplitude ◽  
Ice Stream ◽  
Long Duration ◽  
Seismographic Network

AbstractThe steep increase in Greenland’s glacial earthquake activity detected by the Global Seismographic Network since the late 1990s suggests that a close inspection of these events might provide clues to the nature and origin of such seismic activity. Here we discuss the detection of large, unexpected seismic events of extraordinarily long duration (10–40 min) occurring about once every 2 days, and localized in the ice stream that feeds the Earth’s fastest-moving glacier (Jakobshavn Isbræ) from the east. These ‘glacial rumblings’ represent an ice-mass wasting process that is greater and more frequent than glacial earthquakes have suggested. Probably triggered by calving, the rumblings are all very similar regardless of duration, and all end with a sharp, earthquake-like event in which the largest seismic amplitude is in the rumbling and that might signal the collapse of large ice masses upstream. By calculating the total amount of seismic energy released as rumblings, we estimate that the maximum seasonal amount of ice moved seismogenically down the ice stream is up to 12 km3, or ∼30% of the average annual iceberg discharge in Jakobshavn.

Do historical rates of seismicity in southern California require the occurrence of earthquake magnitudes greater than would be predicted from fault length?

1997 ◽  
Vol 87 (6) ◽  
pp. 1662-1666 ◽  
Author(s):  
Mark W. Stirling ◽  
Steven G. Wesnousky
Keyword(s):  
Working Group ◽  
Southern California ◽  
Active Faults ◽  
Historical Seismicity ◽  
Historical Distribution ◽  
Large Earthquakes ◽  
Fault Length

Abstract The Working Group on California Earthquake Probabilities reported a discrepancy between the historical rates of large earthquakes in southern California and rates predicted from interpretation of geological, geodetic, and historical seismicity data. It was suggested that the discrepancy may be due to the assumption within their analysis that the magnitude of the largest earthquake on a fault is limited by the mapped fault length. Our analysis of the available data does not support the presence of a historical deficit in the rate of seismicity, nor does it require that earthquakes that rupture beyond the lengths of mapped active faults in southern California, or that rupture numerous subparallel faults, are needed to explain the historical distribution of seismicity.

scholarly journals SAKHALIN

2020 ◽  
pp. 152-161
Author(s):  
T. Fokina ◽  
D. Safonov ◽  
D. Kostylev ◽  
V. Mikhaylov
Keyword(s):  
Seismic Activity ◽  
Focal Mechanisms ◽  
Local Network ◽  
Seismic Events ◽  
Regional Network ◽  
Strong Earthquakes ◽  
Seismic Regime ◽  
Seismic Stations ◽  
Macroseismic Effect

A review of the Sakhalin seismicity in 2014 based on the data of regional network is given. The network included four stationary and ten temporary digital seismic stations. This network was supported by ten stations of local network operating in the south of Sakhalin. Parameters of 450 seismic events, including 25 explosions, and focal mechanisms for 4 events are determined. 22 earthquakes had a macroseismic effect. The map of earthquake completeness and the map of epicenters are given. The distribution of crust and deep earthquakes on magnitude and their summarized energy for seven seismoactive areas in comparison with average parameters for 2001–2013 are presented. For each area and the region as a whole, an analysis of the seismic regime parameters in 2014 in comparison with long-term parameters is given, tangible and strong earthquakes are described. The seismicity of the Sakhalin region in 2014 can be characterized as a moderate one. Somewhat increased seismic activity was recorded in the East Sakhalin and Southeastern areas.

Seismic activity along a Cretaceous magmatic intrusion in Monchique, SW Iberia

2020 ◽  
Author(s):  
Analdyne Soares ◽  
Susana Custódio ◽  
Marta Neres ◽  
Dina Vales ◽  
Luís Matias
Keyword(s):  
Seismic Activity ◽  
Active Faults ◽  
Plate Boundary ◽  
Velocity Model ◽  
Historical Record ◽  
Focal Mechanisms ◽  
Magmatic Intrusion ◽  
Mainland Portugal ◽  
3D Velocity Model ◽  
Paleozoic Rocks

<p>Iberia, located at the southwestern end of Europe, displays a complex pattern of seismic activity, with most known active faults slipping at low rates (< 1 mm/yr). However, the seismic activity is remarkable, with numerous earthquakes in the historical record proving destructive. The earthquake cluster in mainland Portugal that has a highest rate of seismic activity is very localized (small spatial extent), extends vertically from 5 to 20 km depth and lays on the Monchique late Cretaceous magmatic intrusion, in SW Portugal. This magmatic intrusion forms strong rheological contrast between the intruded magmatic rocks and surrounding Paleozoic rocks. Furthermore, it is the locus of abundant natural water springs. Several pertinent questions remain to be answered concerning earthquakes in Monchique: Are earthquakes in Monchique simply a response to tectonic stresses (given the proximity of Monchique to the EU-AF plate boundary), with the localization of brittle failure in the region facilitated by the rheological contrast between the Cretaceous intrusion and surrounding Paleozoic rocks? Do fluids play a role in facilitating slip in existing fractures? Or, conversely, is the circulation of fluids facilitated by the faulting that results from the rheological contrasts? Are there hazardous faults in Monchique? In this presentation, we re-analyze in detail the seismic data recorded by the regional permanent seismic network, in order to better understand the relationship between seismic activity and igneous intrusion. In particular, we re-locate earthquakes using NonLinLoc and PRISM3D, a 3D velocity model for the region. At a subsequent step, we re-locate earthquakes using HypoDD. We also perform a clustering analysis based on waveform similarity and compute focal mechanisms for the region. The results show that earthquakes align along two main directions, E-W and NNE-SSW, coinciding with surface features of the magmatic intrusion. Focal mechanisms indicate dominantly strike-slip faulting, with the possible fault planes coinciding with the favored directions of earthquake lineations. We investigate the spatio-temporal evolution of seismicity and address possible forcing mechanisms, including tidal forcing.</p><p> </p><p> </p><p><span>The author would like to acknowledge the financial support  FCT through project</span><span> UIDB/50019/2020 </span>– IDL and PTDC/GEO-FIQ/2590/2014 - SPIDER.</p>

scholarly journals General regularities of seismic activity of Northern Armenia in connection with block structure and tectonic activity

2020 ◽  
Vol 11 (3) ◽  
pp. 595-605
Author(s):  
K. S. Ghazaryan ◽  
R. S. Sargsyan
Keyword(s):  
Spatial Distribution ◽  
Seismic Activity ◽  
Block Structure ◽  
Focal Mechanisms ◽  
Tectonic Activity ◽  
Seismic Events ◽  
Long Period ◽  
Fault Structures ◽  
Block Structures ◽  
Regular Patterns

The study is focused on searching for spatial regularities in the occurrence of earthquake hypocenters in different geological settings in Northern Armenia. Tectonic-geomorphological indices are applied to define the tectonic activity of blocks composing the study area, which was manifested within a long period of time, starting from the neotectonic development period. The blocks are classified accordingly. The regional seismic activity is analysed considering the block structure of the study area. Earthquake focal mechanisms are determined, and dominant displacement trends are identified. Based on the comparative analysis of the blocks’ tectonic activity indicators and the locations of seismic events differing in strength, regular patterns of spatial distribution of seismic events are identified. It is established that the earthquake hypocenters of different strength occur in certain block structures; and the predominant types of movements in the earthquake hypocenters are largely determined by types of fault structures. It is emphasized that investigating the blocks’ neotectonic activity is important for discovering the general patterns of spatial distribution of seismic events.

Interactions of Earthquakes in Central Italy over the Past 100 Yr through Coulomb Stress Changes, and Implications for Seismic Hazards

2020 ◽  
Vol 110 (1) ◽  
pp. 178-190 ◽  
Author(s):  
Bin Shan ◽  
Yashan Feng ◽  
Chengli Liu ◽  
Xiong Xiong
Keyword(s):  
Central Italy ◽  
Active Faults ◽  
Earthquake Hazard ◽  
Seismic Hazards ◽  
Historical Seismicity ◽  
Normal Faults ◽  
Coulomb Stress Changes ◽  
Earthquake Hazard Assessment ◽  
Stress Changes ◽  
Large Earthquakes

ABSTRACT Italy has a historical earthquake record that is complete for events with a magnitude above 5.8 since A.D. 1349, making it possible to study Coulomb failure stress changes (ΔCFS) over a long period. In this study, we investigated the interactions between moderate-to-large earthquakes through ΔCFS over 100 yr in central Italy. This region is characterized by intense seismicity with predominantly extensional components. Hence, earthquake hazard assessment is of great public concern. Besides, earthquake interactions on normal faults are relatively less studied compared to reverse and strike-slip faults. ΔCFS calculations in this study incorporated both coseismic stress transfer and postseismic viscoelastic relaxation, and found the epicenters of 13 out of 15 events located in positively stressed lobes induced by previous earthquakes, confirming a correlation between the ΔCFS pattern and locations of moderate-to-large earthquakes. Next, we estimated the current distribution of ΔCFS on active faults, and after a comprehensive analysis of ΔCFS accumulation, slip rates, historical seismicity, and locations of populated cities, we identified three regions of potential seismic hazards in this region.

scholarly journals A decade of progress in seismology since the Edgecumbe earthquake

1997 ◽  
Vol 30 (2) ◽  
pp. 163-166
Author(s):  
Euan G. C. Smith
Keyword(s):  
New Zealand ◽  
Site Response ◽  
Active Faults ◽  
Strong Motion ◽  
Historical Seismicity ◽  
Ground Acceleration ◽  
Earthquake Catalogues ◽  
Motion Data ◽  
Moderate Earthquake ◽  
Large Earthquakes

During the decade, the contemporaneous increase in data from moderately large earthquakes in New Zealand (and overseas) and the re-equipping of the New Zealand seismograph and accelerograph networks has seen good progress on several fronts. Earthquakes are now more accurately located and their spatial distribution is better defined. There have been improvements in the various databases used for seismic hazard assessments: active faults, earthquake catalogues, historical seismicity, and strong ground motions. The increase in strong-motion data has enabled the development of better models for Peak Ground Acceleration, and the effect of site conditions on site response, particularly for weak-to-moderate earthquake motions, has been studied in detail.

scholarly journals Revelation of Potentially Seismic Dangerous Tectonic Structures in a View of Modern Geodynamics of the Eastern Caucasus (Azerbaijan)

2021 ◽  
Author(s):  
Talat Kangarli ◽  
Tahir Mammadli ◽  
Fuad Aliyev ◽  
Rafig Safarov ◽  
Sabina Kazimova
Keyword(s):  
Stress State ◽  
Active Faults ◽  
Focal Mechanisms ◽  
Seismic Events ◽  
Tectonic Structures ◽  
The North ◽  
Potential Source ◽  
Deep Faults ◽  
Source Zones ◽  
Lateral Displacements

The stress state of the earth’s crust in the Eastern Caucasus, located in the zone of collision junction of the North Caucasian, South Caucasian, and Central Iranian continental massifs, is a consequence of the inclusion of the Arabian indenter into the buffer structures of the southern framing of Eurasia at the continental stage of alpine tectogenesis. This evidenced from the results of geophysical observations of the structure and seismic-geodynamic activity of the region’s crust. The latter, at the neotectonic stage, was presented as underthrust of the South Caucasian microplate under the southern structures of Eurasia. The analysis and correlation of historical and recent seismic events indicate the confinement of most earthquake foci to the nodes of intersection of active faults with various orientations or to the planes of deep tectonic ruptures and lateral displacements along unstable contacts of material complexes of various competencies. The focal mechanisms of seismic events reveal various rupture types, but in general, the earthquake foci are confined to the nodes of intersection of faults of the general Caucasian and anti-Caucasian directions. Based on the observed weak seismicity, active areas of deep faults were identified, which are accepted as potential source zones.

scholarly journals BAYKAL and TRANSBAIKALIA

2019 ◽  
Author(s):  
Valentina Melnikova ◽  
N. Gileva ◽  
O. Masalskii
Keyword(s):  
Seismic Activity ◽  
Rift Zone ◽  
Baikal Rift Zone ◽  
Strike Slip ◽  
Focal Mechanisms ◽  
Normal Faults ◽  
Seismic Events ◽  
High Degree ◽  
South Baikal

The seismicity of Pribaikalye and Transbaikalia in 2013 is reviewed. 6706 earthquakes with КР≥5.6 were recorded there during that year. Most of them (92 %) are located in the Baikal rift zone. The high degree of clustering of seismic events is observed in South Baikal and Baikal-Muja areas. The largest earthquake with Mw=4.3 was in the Baikal-Muja area. Focal mechanisms of 47 earthquakes (КР9.6) were determined in 2013. Most of them correspond to normal faults, with strike-slip component contribution in some cases. Overall, the rate of seismic activity observed in Pribaikalye and Transbaikalia in 2013 was low.

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