1,721,029 research outputs found
The 17 October 2005 earthquakes at the Gulf of Sigacik (western Turkey): directivity and slip models for the strongest events
No full textThe October 2005 series of earthquakes that occurred in the Gulf of Si˘gaçik (western Turkey) reveal the operation of pure strike-slip faults in a region dominated by N-S extension and bounded by well-documented graben structures. The sequence is characterized by the occurrence of three moderate size events (17 October 2005, 05:45 UTC, Mw 5.4; 17 October 2005, 09:46 UTC, Mw 5.8; and 20 October 2005, 21:40 UTC, Mw 5.8) with an eastward propagation of occurrence and close spatial separation (<6 km). Aftershocks obtained from high-quality local network (Aktar et al., 2006 in review) generally are aligned along an ENE-WSW direction, however they also revealed activation of NE-SW trending structures, close to the epicenter of the 1st event, which imply sinistral strike-slip sense of motion. Thus, the identification of the fault plane, at least for this event, is crucial for the interpretation of the sequence. As the distribution of aftershocks was puzzling, because it is not clear whether the NE-SW aftershocks cloud should be considered as off-fault aftershocks, or aftershocks related to the fault plane, here we explore the presence of any directivity effects related to the propagation of these events that would shed light to the identification of the fault plane. Thus, at first we estimate source time functions through an empirical Green's function approach to examine the variation of their shape with azimuth around the source and afterwards we invert their shapes to examine the spatial and temporal distribution of the slip on the main fault. Due to the location of these events at the cross-boundary between Greece and Turkey we used broadband records from the National Seismographic Networks of both countries that provided adequate coverage in azimuth of the activated area. The shape of the source time functions (STF's) of the first event of 17 October 2005, 05:45 UTC, Mw 5.4, exhibit clear directivity towards SW, which strongly implies that from the two nodal planes the NE-SW trending one is the fault plane, whereas the STF's for the stations lying on the north and south of the epicenter are similar, exhibiting no directivity effects. No clear directivity effects were observed for the two other strong events of the sequence. The distribution of the slip onto the fault planes for the three strong events revealed that in all cases the moment was released in one significant slip patch extending in depth from 2 km to 10 km. The maximum slip was 40cm for the first event and 2 m for the other two events of the sequence. The existence of geothermal activity in the activated region implies that it is in an unstable state, with the fault systems close to rupture and very sensitive to stress perturbations and supports the simultaneous activation of multiple structures
Source characteristics of the 8 January 2006 (Mw 6.7) intermediate depth Kythera earthquake
No full textThe 8 January 2006, M 6.7 intermediate depth Kythera earthquake: Focal mechanism of the mainshock and slip distribution model using teleseismic waveforms.
No full textSource process of the 14 February 2008 M6.7 Earthquake Offshore South Peloponnese (Greece)
No full textWe investigate the rupture process of the 14 February 2008, M6.7 earthquake sequence that occurred offshore the westernmost tip of the Peloponnese peninsula in southern Greece. The sequence occurred close to the western boundary of the subducting African lithosphere with the overlying Aegean crust. Three were the strongest events of the sequence: 14 Feb 2008 M6.7 depth 30 km, low-angle (10o) thrust, its strongest aftershock on the same day and two hours later of M6.1 depth 33km, again low angle thrust and on 20 Feb 2008 M6.0 a strike-slip event at shallow 10 km depth. The operation of the low-angle thrust, at 30 km and just above it, at 10 km, of the strike-slip structure, was nearly simultaneous. We used the M6.1 aftershock as empirical Green's function (EGF) to invert for the slip distribution of the strongest M6.7 event of the sequence. We were able to identify the low-angle plane (strike 288o, dip 10o and rake 73o) as the fault plane, in accordance with previous knowledge. The slip model is dominated by two distinct slip patches, which extend to the SSE of the hypocenter thus implying rupture directivity toward that direction. This result is further supported by both the teleseismic waveform inversion results and the shapes of the computed source time functions at different azimuths around the epicentral area. Maximum slip is estimated at 270 cm, while average slip on the ruptured area (3422 km) was 70 cm. Optimum values for the rise time for this event are estimated around 1.5 sec, i.e. larger that what would be expected based on empirical relations. This is believed to be another factor, apart from the offshore location of the epicentre, for the low levels of strong ground motion observed in the mezoseismal area
Synthetic tests to explore the resolution of slip models obtained from the inversion of teleseismic waveforms: complex and segmented rupture of the 14 August 2003, Mw6.2 Lefkada (Ionian Islands) earthquake
No full textComplex and segmented rupture of the 14 August 2003 (Mw 6.2) Lefkada (Ionian Islands) earthquake
No full textThe 14 August 2003 (Mw 6.2) Lefkada earthquake ruptured the Lefkada Segment of the Cephalonia Transform Fault Zone (CTFZ) a major structure along the Ionian Islands of Greece.We invert 30 P and 9 S waves recorded by the Global Seismographic Network to recover the slip distribution of the earthquake. Teleseismic (Benetatos et al., 2004) and regional (Zahradnik et al., 2004) waveform modelling has revealed the multiple (mainly double) source character of the mainshock, and our preferred model indicates a) the earthquake occurred as two distinct events, separated in space (40 km) and time (14 sec), b) the moment was released in three distinct patches (asperities). The first patch of moment released is located underneath the western coast of Lefkada Island confined in a small area ( 25 × 10 km2) and at depths below 12 km. The second patch of moment release is located further south in the sea, close to the northern coast of Cephalonia Island and is confined in an even smaller area ( 15 × 10 km2). The third patch of moment released occurred in the area between the two fault segments considered, which corresponds to the intersection of the Lefkada and Cephalonia Segments of CTFZ. A maximum slip of 34 cm was observed on the north segment beneath Lefkada Island. In order to obtain satisfactory fit to the teleseismic body waves the contribution from subevents on both segments has to be considered. Shakemaps of peak ground velocities (PGV), simulated from the slip model around the epicentral region, especially on the western coast of Lefkada Island, are in good agreement with the distribution of reported damage and intensity level of VII. The displacement field on the surface calculated using forward modelling shows very small values and limited subsidence of the northern parts of Lefkada and Cephalonia Islands. Descriptions of historical events indicate that sequential and segmented rupture of the Lefkada CTFZ has occurred in the past, and the strength of the fault seems variable, with the southern part being stronger and more resistant to rupture than in the north
The 14 February 2008 earthquake (M6.7) sequence offshore south Peloponnese (Greece): Source models of the three strongest events
No full textStochastic strong ground motion simulation of intermediate depth earthquakes: The cases of the 30 May 1990 Vrancea (Romania) and of the 22 January 2002 Karpathos Island (Greece) earthquakes
No full textTime Domain Moment Tensors for shallow (h < 40 km) earthquakes in the broader Aegean Sea for the years 2006 and 2007: the database of the Aristotle University of Thessaloniki
No full textActive seismic deformation in the Italian peninsula and Sicily
No full textRecent and historical seismicity as well as reliable fault plane solutions are used in order to perform a moment tensor analysis and estimate the active crustal and sub-crustal deformation of the Italian peninsula and Sicily. The results show that in Northern Italy, along the Alps, the deformation is taken up by compression at N162°E and a rate of 1 mm/yr. The thickening of the seismogenic layer is taking place at a rate of 0.1 mm/yr. In Central Italy, along the Apennines, extension is prevailing at N28°E and a rate of 3 mm/yr which causes thinning of the seismogenic layer at a rate 0.5 mm/yr. In Southern Italy, at Calabria, the deformation is taken up as extension at N40°E and a rate of 11 mm/yr. At the island of Sicily, compression is occurring at N25°E and a rate of 1 mm/yr. These results are in agreement with plate motion models for the area. The analysis of the deep seismicity of the Tyrrhenian Sea showed that the descending slab is in a state of down dip compression at N146°E and a rate of 2 mm/yr.JCR Journalope
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