Microearthquakes in the TDP swarm, Turkey: clustering in space and time

Lovell, John H.; Crampin, Stuart; Evans, Russ; Üçer, S. Balamir

doi:10.1111/j.1365-246x.1987.tb05229.x

Cited by 14 publications

(6 citation statements)

References 26 publications

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“…Although the Kandilli Observatory, Bogaziçi University, has established the MAR-NET seismic network for microearthquake observations (Ü çer et al, 1985), this network could not cover the whole seismic gap region. According to previous studies, microearthquake activity in the seismic gap region has been very low in general, except for some swarm areas (Crampin et al, 1985;Evans et al, 1987;Tsukuda et al, 1988;Lovell et al, 1989;Nishigami et al, 1990;Iio et al, 1991), but detailed characteristics have not been very clear without a dense network covering the seismic gap region.…”

Section: Introductionmentioning

confidence: 94%

Aftershock Activity of the 1999 Izmit, Turkey, Earthquake Revealed from Microearthquake Observations

Ito¹,

Üçer²,

Barış³

et al. 2002

Bulletin of the Seismological Society of America

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An accurate aftershock distribution of the 1999 İzmit, Turkey, earthquake was obtained by using the data from a local seismic network, IZINET, and 10 temporary seismic stations. More than 2000 aftershocks were relocated for the period of about 2 months following the mainshock. From this aftershock distribution we obtained several pieces of information on the characteristics of the mainshock. First, the mainshock initiated fault rupture from a place adjacent to an active swarm area where many microearthquakes had been occurring for more than 20 yr prior to the mainshock. Second, the aftershock region extended in the east-west direction along the North Anatolian Fault Zone (NAFZ). This confirms that the mainshock was caused by a slip on the NAFZ. Third, the western end of the rupture caused by the mainshock is likely to have reached up to about 29.2Њ E in the İzmit Bay, and hence the total length of the fault rupture caused by the mainshock amounts to about 150 km, as long as the estimate of the fault rupture length is based on the aftershock distribution. This information is important for the discussion on the possibility of future large earthquakes in the west of the source region of the İzmit earthquake. We also found a clear tendency that aftershocks occur in clusters, which implies strong heterogeneity in both the rupture process and the medium along the fault zone.

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Section: Introductionmentioning

confidence: 94%

Aftershock Activity of the 1999 Izmit, Turkey, Earthquake Revealed from Microearthquake Observations

Ito¹,

Üçer²,

Barış³

et al. 2002

Bulletin of the Seismological Society of America

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“…It has been well known that seismicity in the northern branch is rather high, as characterized by clustering of small earthquakes in some areas Evans et al, 1987;Lovell et al, 1989). In contrast, seismicity has been extremely low in the southern branch (Tsukuda et al, 1988;Nishigami et al, 1990;Iio et al, 1991).…”

Section: Seismicity Before the Mainshockmentioning

confidence: 99%

Preliminary results of multidisciplinary observations before, during and after the Kocaeli (Izmit) earthquake in the western part of the North Anatolian Fault Zone

et al. 2014

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On August 17, 1999, a destructive earthquake occurred in the western part of the North Anatolian Fault Zone, Turkey. The earthquake source region has been designated as a seismic gap and an M7-class earthquake has been supposed to occur someday in the future so as to fill this seismic gap. So far we have undertaken various kinds of observations in this area and we could obtain some valuable data before, during and after the mainshock. Here we report some of the preliminary results of our recent studies, which include field work started in late July this year and continued during and after the earthquake occurrence just in the earthquake source region and its vicinity, in addition to seismic observations carried out for several years before the mainshock. Much emphasis is put on magnetotelluric field data acquired during the mainshock; in fact, large variations caused by seismic waves were recorded. Such variations could be interpreted in terms of electromagnetic induction in the conducting crust caused by the velocity field interacting with the static magnetic field of the Earth. In particular, the first motion of seismic wave could be identified in the records and used for precise determination of the hypocenter of the mainshock.

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“…Crampin have shown that the parallel polarizations of the first split shear-waves can be consistently interpreted in terms of propagation through a distribution of vertical liquid-filled cracks aligned approximately N 100°E. This orientation is consistent with cracks opening normal to the approximately north-south axis of minimum compression, which has been identified from fault-plane solutions Crampin & Evans 1986;Lovell et al 1987). Shear waves which propagate through such a system of approximately east-west oriented vertical cracks will split and, at angles of incidence within the shear-wave window, the first-arriving (faster) split shear-wave will be polarized in the N 100°E plane of the cracks .…”

Section: Crack-induced Anisotropymentioning

confidence: 56%

Shear-wave polarizations near the North Anatolian Fault - III. Observations of temporal changes.

Chen

Booth

Crampin

1987

Geophysical Journal International

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Almost all shear-waves from local earthquakes recorded on closely-spaced three-component seismometer networks deployed near the North Anatolian Fault, Turkey, in two experiments in 1979 and 1980, display shear-wave splitting. The observations are consistent with the presence of EDA (extensive-dilatancy anisotropy), distributions of fluid-filled cracks and microcracks aligned by the regional stress field. Temporal changes in the stress-field, which may occur before an earthquake, may modify the geometry and possibly the orientation of the EDA-microcracks, and lead to corresponding changes in the behaviour of the split shear-waves. A third experiment was undertaken in 1984 to investigate EDA further and to search for possible temporal variations of the polarization of the leading split shearwave and the time delay between split shear-waves. Observations indicate that the polarization alignments, which are parallel to the strike of the parallel vertical EDA-cracks, are unaltered between 1979 and 1984, implying that the direction of the regional stress field has not changed significantly. Temporal changes in the stress field are more likely to cause changes in the crack density and/or aspect ratio, which would result in a corresponding change in time delay between the split shear-waves. We examine observations of time delay in relation to their propagation path with respect to the crack geometry since i t is then possible to separate the effects of changes in crack density and changes in aspect ratio. With this procedure, a small temporal variation of time delays is found between 1979 and 1984, consistent with a decrease in crack density, and consequently a relaxation of stress, in this time period. No evidence was found for any observable variation of time delay over a six month observation span in 1984. We suggest that analysis of repeated shear-wave VSPs offers a technique for monitoring stress changes before earthquakes.

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Microearthquakes in the TDP swarm, Turkey: clustering in space and time

Cited by 14 publications

References 26 publications

Aftershock Activity of the 1999 Izmit, Turkey, Earthquake Revealed from Microearthquake Observations

Aftershock Activity of the 1999 Izmit, Turkey, Earthquake Revealed from Microearthquake Observations

Preliminary results of multidisciplinary observations before, during and after the Kocaeli (Izmit) earthquake in the western part of the North Anatolian Fault Zone

Shear-wave polarizations near the North Anatolian Fault - III. Observations of temporal changes.

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