| 2014年11月22日康定M6.3级地震序列发震构造分析 |
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| 引用本文： | 易桂喜,龙锋,闻学泽,梁明剑,王思维.2014年11月22日康定M6.3级地震序列发震构造分析[J].地球物理学报,2015,58(4):1205-1219. |
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| 作者姓名： | 易桂喜 龙锋 闻学泽 梁明剑 王思维 |
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| 作者单位： | 1. 四川省地震局, 成都 610041;
2. 四川赛思特科技有限责任公司, 成都 610041;
3. 地震动力学国家重点实验室, 中国地震局地质研究所, 北京 100029;
4. 中国地震局地质研究所, 北京 100029 |
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| 基金项目： | 四川赛思特科技有限责任公司西部大开发优惠政策节税资金投资项目(XDK2015001),国家科技支撑计划(2012BAK19B01-01),国家重点基础研究计划(973)(2008CB425701),中国地震局2015年地震大形势跟踪研究专项经费共同资助. |
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| 摘 要： | 2014年11月22日在NW向鲜水河断裂带中南段四川康定县发生M6.3级地震,11月25日在该地震震中东南约10km处再次发生M5.8级地震.基于中国国家数字地震台网和四川区域数字地震台网资料,采用多阶段定位方法对本次康定M6.3级地震序列进行了重新定位;利用gCAP(generalized Cut And Paste)矩张量反演方法获得了M6.3和M5.8级地震的震源机制解与矩心深度,分析了本次地震序列的发震构造,并结合历史强震破裂时空分布和2001年以来小震重新定位结果,对鲜水河断裂带中段强震危险性进行了初步探讨.获得的主要结果如下:(1)M6.3级主震震中位于101.69°E、30.27°N,震源初始破裂深度约10km,矩心深度9km;M5.8级地震震中位于101.73°E、30.18°N,初始破裂深度约11km,矩心深度9km.gCAP矩张量反演结果揭示这两次地震双力偶分量占主导,M6.3级地震的最佳双力偶解节面Ⅰ走向143°/倾角82°/滑动角-9°,节面Ⅱ走向234°/倾角81°/滑动角-172°.M5.8级地震最佳双力偶解节面Ⅰ走向151°/倾角83°/滑动角-6°,节面Ⅱ走向242°/倾角84°/滑动角-173°.依据余震分布长轴展布与断裂走向,判定节面Ⅰ为发震断层面,M6.3和M5.8级地震均为带有微小正断分量的左旋走滑型地震.(2)序列中重新定位的459个地震平均震源深度约9km,地震主要集中分布在6~11km深度区间,余震基本发生在M6.3和M5.8级地震震源上部.依据余震密集区展布范围,推测本次康定地震的震源体尺度长约30km、宽约4km、深度范围约6km.M6.3级主震震源附近的余震稀疏区可能是一个较大的凹凸体(asperity),在主震中能量得以充分释放.(3)最初3天的余震主要分布在M6.3级地震NW侧;而M5.8级地震之后的余震主要集中在其震中附近.M6.3级地震以及最初3天的绝大部分余震发生在倾角约82°近直立的NW走向色拉哈断裂上;M5.8级地震与其后的多数余震发生在倾角约83°近直立的NW走向折多塘断裂北端走向向北偏转部位,M5.8级地震可能是M6.3级地震触发相邻的折多塘断裂活动所致.(4)康定M6.3与M5.8级地震发生在鲜水河断裂带乾宁与康定之间的色拉哈强震破裂空段,本次地震破裂尺度较小,尚不足以填补该强震空段.色拉哈段以及相邻的乾宁段7级地震平静时间均已超过其平均复发周期估值,未来几年存在发生7级地震的危险.康定M6.3级地震序列基本填补了震前存在于塔公与康定之间的深部小震空区,未来强震发生在塔公至松林口段深部小震稀疏区内的可能性很大.
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| 关 键 词： | 康定M6.3级地震序列 重新定位 震源机制 发震构造 强震危险性 |
| 收稿时间： | 2014-12-09 |
Seismogenic structure of the M6.3 Kangding earthquake sequence on 22 Nov. 2014, Southwestern China |
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| YI Gui-Xi,LONG Feng,WEN Xue-Ze,LIANG Ming-Jian,WANG Si-Wei.Seismogenic structure of the M6.3 Kangding earthquake sequence on 22 Nov. 2014, Southwestern China[J].Chinese Journal of Geophysics,2015,58(4):1205-1219. |
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| Authors: | YI Gui-Xi LONG Feng WEN Xue-Ze LIANG Ming-Jian WANG Si-Wei |
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| Institution: | 1. Earthquake Administration of Sichuan Province, Chengdu 610041, China;
2. Sichuan Seistech Corporation Ltd., Chengdu 610041, China;
3. State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing 100029, China;
4. Institute of Geology, China Earthquake Administration, Beijing 100029, China |
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| Abstract: | On 22 Nov. 2014, an M6.3 earthquake hit Kangding County in Sichuan Province, southwestern China. 3 days later, another M5.8 earthquake occurred in the same region, about 10 km southeastwards from the epicenter of the M6.3 mainshock. Both earthquakes were on the NW-striking Xianshuihe fault zone where no M≥6.0 earthquakes were reported after the 1982 M6.0 Ganzi event. From the relocated aftershock distribution and focal mechanism solutions, we aim to analyze the seismogenic structure of the 2014 M6.3 Kangding 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 strong-earthquake 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 M6.3 and M5.8 earthquakes were inverted simultaneously by the gCAP (generalized Cut and Paste) moment tensor inversion method. The spatial-temporal distribution of the M≥6.5 strong 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 9 km; the relocated M5.8 earthquake is at 101.73°E、30.18°N with the initial rupture depth at about 11 km and the centroid depth of 9 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 plane Ⅰ, and strike 234°, dip 81°, rake -172° for nodal plane Ⅱ for the M6.3 earthquake. For the M5.8 earthquake, the parameters are listed as, strike 151°, dip 83°, rake -6° for the nodal plane Ⅰ, and strike 242°, dip 84°, rake -173° for the nodal plane Ⅱ. Most aftershocks during the first 3 days were distributed on the NW side of the M6.3 mainshock, and majority of the aftershocks after M5.8 earthquake were concentrated around the epicenter of the M5.8 event. 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 6~11 km and most of the aftershocks are shallower than the M6.3 and M5.8 earthquakes. The seismic source scale is estimated to be about 30 km in length and 4 km in width with 6 km in depth according to the aftershock distribution. On the space-time diagram of the historical M≥6.5 strong earthquake ruptures, we observe a gap on the Selaha fault of the central Xianshuihe fault zone, where no M≥6.5 earthquakes occurred since the 1748 M61/2 event. Aseismic gap below the depth 7 km between Kangding and Tagong and a low-seismicity region below the depth 2 km 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 planeⅠof the focal mechanism solution was interpreted as the coseismic rupture plane for the M6.3 and M5.8 earthquakes based on the aftershock distribution and the fault strike. Both earthquakes are of left-lateral strike-slip faulting with some normal component. The relocated M6.3 earthquake 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 M5.8 earthquake and its adjacent aftershocks are on the northern portion of the NW-striking Zheduotang fault with a dip angle of 83°, implying that the M5.8 earthquake on the Zheduotang fault may be induced by the M6.3 earthquake in the adjacent Selaha fault. The scarce aftershock region around the M6.3 mainshock may belong to a relatively large asperity where the accumulated energy was totally released as the M6.3 mainshock occurred. The 2014 M6.3 Kangding 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 M6.3 and M5.8 earthquakes 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 7 km between Kangding and Tagong along the central-southern Xianshuihe fault zone was filled by the 2014 M6.3 Kangding 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. |
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| Keywords: | M6 3 Kangding earthquake sequence Relocation Focal mechanism Seismogenic structure Strong-earthquake risk |
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