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Tuzla earthquake swarm in Turkey

Komut Tolga, Baysal Rıza

Acta Geophysica

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2022

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Vol. 70, no 3

1037--1045

EN

Long-lasting earthquake clusters are common in western Anatolia. One of them has been active in the southwestern part of the Biga peninsula. We had studied this cluster in terms of strain energy produced over time and revealed its interesting characteristics. The seismicity in this clustering region is not normal in terms of both the number of earthquakes, duration of the activity, magnitude/frequency and mainshock/aftershock relations, and the strain energy produced. An abnormal seismic activity with a set of medium-sized earthquakes without a mainshock, which are indistinguishable in size occurred in this clustering region in 2017. Interesting features that are characteristic of earthquake swarms are probably related to the abnormal physical properties of the crust. The 2017 Tuzla activity, where there is also no notable aftershock activity, could be associated with a phase of the swarming phenomenon itself. For this, we approached the 2017 activity in terms of the fact that it may not be part of the active tectonic system. Apart from the presence of high geotherm and hot springs in the region, the crust has been weakened by pre-existing intense fault zones that have developed in previous deformation regimes since the paleo-tectonic periods. Historical and instrumental period large earthquakes have caused loss of life and property in Biga peninsula due to an existing active fault zone. The Tuzla region probably is in this zone extending NE-SW in the peninsula. However, it is very difficult or impossible to distinguish possible foreshocks or precursory phenomenon of a future large earthquake from the background activity of the earthquake swarms.

2

Analysis of microseismicity associated with the 2017 seismic swarm near the Aegean coast of NW Turkey

Mesimeri M., Kourouklas C., Papadimitriou E., Karakostas V., Kementzetzidou D.

Acta Geophysica

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2018

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Vol. 66, no. 4

479--495

EN

A thorough spatiotemporal analysis of the intense seismic activity that took place near the Aegean coast of NW Turkey during January–March 2017 was conducted, aiming to identify its causative relation to the regional seismotectonic properties. In this respect, absolute and relative locations are paired and a catalog consisting of 2485 events was compiled. Relative locations are determined with high accuracy using the double-difference technique and differential times both from phase pick data and from cross-correlation measurements. The spatial distribution of the relocated events revealed a south-dipping causative fault along with secondary and smaller antithetic segments. Spatially, the seismicity started at the westernmost part and migrated with time to the easternmost part of the activated area. Temporally, two distinctive periods are observed, namely an early period lasting 1 month and a second period which includes the largest events in the sequence. The investigation of the interevent time distribution revealed a triggering mechanism, whereas the ETAS parameters show a strong external force (l[1), which might be attributed to the existence of the Tuzla geothermal field.

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Wavelet-based multifractal analysis of earthquakes temporal distribution in Mammoth Mountain volcano, Mono County, Eastern California

Zamani A, Azar A.P, Safavi A.A.

Acta Geophysica

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2014

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Vol. 62, no. 3

585--607

EN

This paper presents a wavelet-based multifractal approach to characterize the statistical properties of temporal distribution of the 19822012 seismic activity in Mammoth Mountain volcano. The fractal analysis of time-occurrence series of seismicity has been carried out in relation to seismic swarm in association with magmatic intrusion happening beneath the volcano on 4 May 1989. We used the wavelet transform modulus maxima based multifractal formalism to get the multifractal characteristics of seismicity before, during, and after the unrest. The results revealed that the earthquake sequences across the study area show time-scaling features. It is clearly perceived that the multifractal characteristics are not constant in different periods and there are differences among the seismicity sequences. The attributes of singularity spectrum have been utilized to determine the complexity of seismicity for each period. Findings show that the temporal distribution of earthquakes for swarm period was simpler with respect to pre- and post-swarm periods.

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Swarms in Andaman Sea, India - a seismotectonic analysis

Mukhopadhyay B., Dasgupta S.

Acta Geophysica

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2008

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Vol. 56, no. 4

1000-1014

EN

The seismotectonic characteristics of 1983–1984, 1993 and 2005 swarms in Andaman Sea are analysed. These swarms are characterised by their typical pulsating nature, oval shaped geometry and higher b values. The migration path of the swarms from north to south along the Andaman Spreading Ridge is documented. While the first two swarms are located along existing mapped rift segments, the 2005 swarm appears to have generated a new rift basin along 8°N. The analysis and supporting evidences suggest that these swarms were generated by intruding magmatic dyke along the weak zones in the crust, followed by rifting, spreading and collapse of rift walls. CMT solutions for 2005 swarm activity indicate that intrusion of magmatic dyke in the crustal weak zone is documented by earthquakes showing strike slip solution. Subsequent events with normal fault mechanism corroborate the rift formation, collapse and its spreading.

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Focal mechanism of earthquakes from the June 1987 swarm in Aswan, Egypt, calculated by the moment tensor inversion

Awad H., Kwiatek G.

Acta Geophysica Polonica

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2005

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Vol. 53, nr 3

275-291

EN

We obtained seismic moment tensor solutions of ten events from the June 1987 earthquake swarm, which occurred along the Kalabsha fault zone in the northern part of the Lake Aswan area in Egypt. In addition, the composite fault plane solution of this sequence was also calculated. The waveform data were obtained from the Aswan seismological network, which consists of 13 field stations with short period seismometers GS-13. The June 1987 swarm was a sequence of microearthquakes (M ? 3.4), shallow (0-10 km) events forming two successive bursts, which took place on June 17 and 19. The moment tensor solutions indicate that the focal mechanisms of events from this swarm sequence are expressed by right-lateral strike slip faults. They represent also an effective east-west compressional stress field acting in the area. Geological and geophysical data demonstrate that the Kalabsha fault zone is a right-lateral strike slip fault that consists of several fault segments trending in the east-west direction, perpendicular to the axis of the main course of the Lake As-wan. Thus, the focal mechanisms of the 1987 events are consistent with the local tectonics of the area.