| Analysis of the 1997 Zirkuh (Ghean-Birjand) aftershock sequence in east-central Iran |
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| 作者姓名： | Mohammad-Reza Gheitanchi Mohammad Raeesi |
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| 作者单位： | Institute of Geophysics，Tehran University，Institute of Geophysics，Tehran University Tehran P.O.Box 13145-1137，Iran，Tehran P.O.Box 13145-1137，Iran |
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| 基金项目： | Research Project from the Institate of Geophysics and Office of the Vice Chancellor for Research of Tehran Univer-sity (651/1/317) |
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| 摘 要： | IntroductionThesouthernpartofKhorasanProvinceineast-centralIranisoneoftheseismicallyactiveregionsintheMiddleeast.Historicalreportsindicatedseveralearthquakeshavecausedseveredestructionsandhumanlossinthisregionduringthepastcenturies(Ambraseys,Melville,1982).Theinstrumentallyrecordedearthquakesaswellastheexistenceofseveralactivefaultsalsosug-gestedthattheregionhadahighpotentialofseismicactivities.OnMay10,1997at07:57:29.6GMT,12:27:29.6localtime,ashallowdestructiveearthquakewithoutanyfeltfores…
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Analysis of the 1997 Zirkuh (Ghean-Birjand) aftershock sequence in east-central Iran |
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| Mohammad-Reza Gheitanchi,Mohammad Raeesi.Analysis of the 1997 Zirkuh (Ghean-Birjand) aftershock sequence in east-central Iran[J].Acta Seismologica Sinica(English Edition),2004,17(1):38-46. |
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| Authors: | Mohammad-Reza Gheitanchi Mohammad Raeesi |
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| Abstract: | In this study, the 1997 Zirkuh (Ghaen-Birjand) locally recorded aftershock sequence was analyzed. On the basis of the distribution of aftershocks, a NW-SE trend vertical faulting with an extension of at least 90 km could be esti-mated. The fault rupture causing the Zirkuh earthquake apparently initiated in the epicentral area and propagated unilaterally to southeast. The cross-section of aftershocks along the fault suggests that the aftershocks had a depth range of 20 km, indicating that the seismic activity was taking place within the upper crust and the seismogenic layer, in this region, had a thickness not greater than 20 km. The distribution of aftershocks suggested that the western block acted as hanging wall during the source process of the main shock. The time-space distribution of aftershocks showed two distinguished gaps coincided with the observed gaps on the surface faulting. It was con-cluded that the first gap acted as a barrier during the main shock and aftershocks, while the deeper part of second gap was ruptured either during the main shock or the aftershocks. The time-frequency pattern of aftershocks decay followed the Modified Omori relations for the first 10 days while the Omori model was best fitted for the later stage of the aftershock sequence. |
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| Keywords: | Zirkuh earthquake seismicity of Khorasan Province source parameters focal mechanism seismotectonics active faults aftershock activity |
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