Spatiotemporal Properties of Seismicity and Variations of Shear-Wave Splitting Parameters in the Western Gulf of Corinth (Greece)

The Western Gulf of Corinth (WGoC) exhibits significant seismicity patterns, combining intense microseismic background activity with both seismic swarms and short-lived aftershock sequences. Herein, we present a catalogue of ~9000 events, derived by manual analysis and double-difference relocation, for the seismicity of the WGoC during 2013–2014. The high spatial resolution of the hypocentral distribution permitted the delineation of the activated structures and their relation to major mapped faults on the surface. The spatiotemporal analysis of seismicity revealed a 32-km-long earthquake migration pattern, related to pore-pressure diffusion, triggering moderate mainshock-aftershock sequences, as fluids propagated eastwards in the course of ~15 months. The anisotropic properties of the upper crust were examined through automatic shear-wave splitting (SWS) analysis, with over 2000 SWS measurements at local stations. An average fast shear-wave polarization direction of N98.8° E ± 2.8° was determined, consistent with the direction of the maximum horizontal regional stress. Temporal variations of normalized time-delays between fast and slow shear-waves imply alterations in the level of stress or microcrack fluid saturation during the long-lasting pore-pressure diffusion episode, particularly before major events. The present study provides novel insights regarding seismicity patterns, active fault structures, anisotropic properties of the upper crust and triggering mechanisms of seismicity in the WGoC.

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Upper crust seismic anisotropy study and temporal variations of shear-wave splitting parameters in the western Gulf of Corinth (Greece) during 2013

Physics of The Earth and Planetary Interiors ◽

10.1016/j.pepi.2017.06.006 ◽

2017 ◽

Vol 269 ◽

pp. 148-164 ◽

Cited By ~ 15

Author(s):

George Kaviris ◽

Ioannis Spingos ◽

Vasileios Kapetanidis ◽

Panayotis Papadimitriou ◽

Nicholas Voulgaris ◽

...

Keyword(s):

Shear Wave ◽

Seismic Anisotropy ◽

Shear Wave Splitting ◽

Temporal Variations ◽

Upper Crust ◽

Gulf Of Corinth ◽

Wave Splitting

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An upper crust shear-wave splitting study for the period 2013-2014 in the Western Gulf of Corinth (Greece)

10.5194/egusphere-egu21-897 ◽

2021 ◽

Author(s):

George Kaviris ◽

Vasilis Kapetanidis ◽

Georgios Michas ◽

Filippos Vallianatos

Keyword(s):

Stress Field ◽

Shear Wave ◽

Shear Wave Splitting ◽

Double Difference ◽

Extension Rate ◽

Upper Crust ◽

Inspection Method ◽

Gulf Of Corinth ◽

Waveform Cross Correlation ◽

Wave Splitting

Seismic anisotropy is investigated by performing an upper crust shear-wave splitting study in the Western Gulf of Corinth (WGoC). The study area, which is a tectonic rift located in Central Greece, is one of the most seismically active regions in Europe, characterized by a 10 to 15 mm/year extension rate in a NNW-SSE direction and E-W normal faulting. Intense seismic activity has been recorded in the WGoC during 2013-2014, including the 2013 Helike swarm, at the southern coast, and the offshore 2014 seismic sequence between Nafpaktos and Psathopyrgos, including an Mw 4.9 event on 21 September 2014. The largest event of the study period was an Mw 5.0 earthquake that occurred in November 2014, offshore Aigion, followed by an aftershock sequence. Seismicity was relocated using the double-difference method, including waveform cross-correlation differential travel-time data, yielding a high-resolution earthquake catalogue of approximately 9000 local events. This dataset was utilized in order to determine the shear-wave splitting parameters in seven stations installed at the WGoC, using a fully automatic technique based on the eigenvalue method and cluster analysis. A smaller subset was analyzed with the visual inspection method (polarigrams and hodograms) for verification of the automatic measurements. All selected station-event pairs were within the shear-wave window and had adequately high signal-to-noise ratio. The orientation of the seismometers of all stations used in the present study has been measured and verified in order to ensure the validity of the obtained fast shear-wave polarization directions and to apply corrections for borehole instruments. Mean anisotropy directions are in general agreement with the horizontal component of the dominant stress field, with some deviations, likely related to mapped faults and local stress anomalies. Temporal variations of time-delays between the two split shear-waves are examined in order to investigate their connection to possible stress field variations, related either to the occurrence of moderate to strong events or to fluid migration.AcknowledgementsWe would like to thank the personnel of the Hellenic Unified Seismological Network (http://eida.gein.noa.gr/) and the Corinth Rift Laboratory Network (https://doi.org/10.15778/RESIF.CL) for the installation and operation of the stations used in the current article. The present research is co-financed by Greece and the European Union (European Social Fund- ESF) through the Operational Programme &#171;Human Resources Development, Education and Lifelong Learning 2014-2020&#187; in the context of the project &#8220;The role of fluids in the seismicity of the Western Gulf of Corinth (Greece)&#8221; (MIS 5048127).

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PRELIMINARY SHEAR-WAVE SPLITTING RESULTS IN THE BROADER AIGION AREA (GREECE) DURING 2013

Bulletin of the Geological Society of Greece ◽

10.12681/bgsg.11821 ◽

2017 ◽

Vol 50 (3) ◽

pp. 1153

Author(s):

G. Kaviris ◽

I. Spingos ◽

V. Kapetanidis ◽

P. Papadimitriou

Keyword(s):

Shear Wave ◽

Anisotropic Medium ◽

Shear Waves ◽

Shear Wave Splitting ◽

Upper Crust ◽

Wave Analysis ◽

Gulf Of Corinth ◽

Wave Splitting ◽

Propagation Media ◽

Seismological Network

An anisotropic upper crust has been revealed in the W. Gulf of Corinth with potentially changing properties. During 2013, a unique opportunity to conduct a shear-wave analysis was presented, as a combination of the significantly increased seismicity in the area, including a seismic swarm between May and August, and the existence of local seismological networks. The Hellenic Unified Seismological Network (HUSN) and the Corinth Rift Laboratory Network (CRLN) provided invaluable data during the unrest period. While shear-waves travel through an anisotropic medium, the splitting phenomenon takes place and, as a result, their propagation is characterized by two discernible components: the fast (Sfast) and the slow (Sslow) one, which arrives to the station in a subsequent temporal point. Modern advances in seismology and geophysics have rendered shear-wave splitting a valuable tool in determining properties of the anisotropic propagation media. One of the predominant causes of this phenomenon is the existence of microcracks throughout the upper crust. The current study presents results for 8 stations from 535 analyzed events that are in agreement with the anisotropy models of EDA and APE.

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