Title: Seismogenic structure of the M6.3 Kangding earthquake sequence on 22 Nov.2014,Southwestern China
Abstract: On 22 Nov.2014,an M6.3earthquake hit Kangding County in Sichuan Province,southwestern China.3days later,another M5.8earthquake occurred in the same region,about10 km southeastwards from the epicenter of the M6.3mainshock.Both earthquakes were on the NW-striking Xianshuihe fault zone where no M≥6.0earthquakes were reported after the 1982M6.0Ganzi event.From the relocated aftershock distribution and focal mechanism solutions,we aim to analyze the seismogenic structure of the 2014 M6.3Kangding earthquake sequence.Along with the analysis on the characteristics of the strong earthquake ruptures and the spatial distribution of the relocated small earthquakes,we will further discuss the future strongearthquake risk between Daofu and Kangding on the central segment of the Xianshuihe fault zone.Based on the digital waveform data from China National Seismic Network and Sichuan Regional Network,the Kangding earthquake sequence was relocated by a multi-step locating method developed by Long et al.The focal mechanism solutions and the centriod depths of the M6.3and M5.8earthquakes were inverted simultaneously by the gCAP(generalized Cut and Paste)moment tensor inversion method.The spatial-temporal distribution of the M≥6.5strong earthquake ruptures since 1725 and the focal depth distribution of relocated small earthquakes from Jan.2001 to Oct.2014 along the central-southern segment of the Xianshuihe fault zone were used to identify the potential seismogenic region of the next strong earthquakes on the segment between Daofu and Kangding.The epicentral relocation of the M6.3 mainshock is at 101.69°E、30.27°N,and its initial rupture depth is about 10 km,while the centroid depth is 9km;the relocated M5.8earthquake is at 101.73°E、30.18°N with the initial rupture depth at about 11 km and the centroid depth of9 km.The moment tensor solutions from gCAP method show that the two events are dominated by the double-couple component.The parameters of the best double-couple solutions are as follows,strike 143°,dip 82°,rake-9°for nodal planeⅠ,and strike 234°,dip 81°,rake-172°for nodal planeⅡ for the M6.3earthquake.For the M5.8earthquake,the parameters are listed as,strike 151°,dip 83°,rake-6°for the nodal planeⅠ,and strike 242°,dip 84°,rake-173°for the nodal planeⅡ.Most aftershocks during the first 3days were distributed on the NW side of the M6.3mainshock,and majority of the aftershocks after M5.8earthquake were concentrated around the epicenter of the M5.8event.The average focal depth of the 459 relocated earthquakes of the sequence is about 9 km.Focal depth distribution reveals that the sequence mainly concentrated in the depth range of 6~11km and most of the aftershocks are shallower than the M6.3and M5.8earthquakes.The seismic source scale is estimated to be about 30 km in length and 4km in width with 6km in depth according to the aftershock distribution.On the space-time diagram of the historical M ≥6.5strong earthquake ruptures,we observe a gap on the Selaha fault of the central Xianshuihe fault zone,where no M≥6.5earthquakes occurred since the 1748M61/2event.Aseismic gap below the depth 7km between Kangding and Tagong and a lowseismicity region below the depth 2km between Tagong and Songlinkou were identified on the vertical cross-section of the relocated small earthquakes since 2001 along the central-southern segment of the Xianshuihe fault zone.The nodel planeⅠ of the focal mechanism solution was interpreted as the coseismic rupture plane for the M6.3and M5.8earthquakes based on the aftershock distribution and the fault strike.Both earthquakes are of left-lateral strike-slip faulting with some normal component.The relocated M6.3earthquake and its aftershocks during the first three days are on the NW-striking Selaha fault with a near-vertical dip angle of 82°,while the M5.8earthquake and its adjacent aftershocks are on the northern portion of the NW-striking Zheduotang fault with a dip angle of83°,implying that the M5.8earthquake on the Zheduotang fault may be induced by the M6.3earthquake in the adjacent Selaha fault.The scarce aftershock region around the M6.3mainshock may belong to a relatively large asperity where the accumulated energy was totally released as the M6.3mainshock occurred.The 2014 M6.3Kangding earthquake sequence occurred within the Selaha strong-earthquake rupture gap between Qianning and Kangding.Due to the duration of quiescence longer than the estimated average recurrence interval for the M7 earthquakes,we propose that the ruptures of the M6.3and M5.8earthquakes are too limited to fill up the gap,posing future M7 earthquake risk on the Selaha and its adjacent Qianning segments along the central segment of the Xianshuihe fault zone.Since most area of the previous seismic gap below the depth 7km between Kangding and Tagong along the central-southern Xianshuihe fault zone was filled by the 2014 M6.3Kangding earthquake sequence,and the most likely place of future strong earthquake occurrence will be below the segment between Tagong and Songlinkou where low seismicity is observed.
Publication Year: 2015
Publication Date: 2015-01-01
Language: en
Type: article
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Cited By Count: 22
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