comparison of locations of rushan earthquake swarm from large and small network

doi:10.3969/j.issn.0253-4967.2015.04.002

Abstract

Abstract:

A notable swarm occurred in Rushan, Shandong Peninsula and its activities continue since Oct. 2013 till now. Up to Sept. 30, 2014, more than 7 000 events have been recorded, in which locatable shocks exceed 2000, and 18 events with M_L≥3.0. The swarm is rarely seen in East China for its extraordinary duration time and surprising high frequency of aftershocks. 18 temporary seismometers have been deployed around the swarm since May 6, 2014, and composed a seismic array for monitoring the swarm activities. Based on data from permanent networks and temporary array, we relocated the earthquake sequence by using hypoDD method. It has been shown that, there is obvious difference between permanent network results and temporary array results. The permanent network of Shandong has a relative large coverage gap(more than 200°)for this swarm. Its location results therefore should not be reliable. There are maybe other errors in the permanent network result due to some problems in the raw data, such as too few stations for most locatable events(3 stations), and relative lower proportion of located events in final result(74.3%, while 95.1% in temporary array result). It can be found by comparing location results from permanent network and temporary array that, using temporary array's data can improve the location accuracy significantly. The results of temporary array are: aftershocks distribution of Rushan swarm is in NWW direction, the dip-direction of fitted fault plane is SW, and the strike and dip angle agree with focal mechanism of the mainshock. Focal depths of aftershocks are at 4.5～8km; the swarm is restricted in a small area about 3km×3km×1km, and has some characteristics such as clustering, staged activities, and etc; the aftershock activities are in accord with crack growth behavior pattern, hence we deduced that there may be fluid intrusion in source area. Finally, we discussed the seismogenic structures and active mechanisms of this swarm combined with relative geologic knowledge. We draw some conclusions as follows: 1)Rushan swarm probably occurred at the boundary of rock bodies of Duogu Mountain and Haiyangsuo super-unit; 2)The seismogenic structure is a blind fault, which should be a part of adjacent Heishankuang-Jilincun Fault, or might be a new fault at rock body boundaries; 3)Rushan swarm might be an evidence for the existence of the disputed Shidao Fault.

Key words: HypoDD, large and small seismic networks, location accuracy, Rushan swarm

摘要：

山东乳山地区自2013年10月起发生震群活动, 并且持续至今(2014年10月); 截至2014年9月30日, 共记录到余震7 000多次, 其中可定位事件2 000多次, M_L≥3.0的18次, 其持续时间、活动频度为1970年以来华东地区罕见。2014年5月6日起, 陆续在现场布设了18个流动台, 持续对序列活动进行观测。基于固定台网和流动台阵的资料, 使用双差方法对地震序列进行重新定位。结果显示, 流动台阵定位结果与固定台网结果存在较大差别, 由于数据本身的问题, 固定台网结果可能存在一定的偏差。流动台阵精定位结果显示, 乳山震群的余震呈NWW向展布, 倾向SW, 与震源机制解结果一致; 余震震源深度较浅, 4.5～8km; 余震主要集中在3km×3km×1km很小的范围内密集活动, 并且具有阶段性、丛集性的特点, 余震活动符合裂纹扩展模式, 可能存在流体触发因素。最后结合有关地质资料对此次乳山震群的发震构造、性质以及震群的活动机理进行了探讨。

关键词: 双差定位, 大小地震台网, 定位精度, 乳山震群

CLC Number:

P315.7

ZHENG Jian-chang, QU Li, QU Jun-hao, HU Xu-hui, LI Dong-mei. comparison of locations of rushan earthquake swarm from large and small network[J]. SEISMOLOGY AND GEOLOGY, 2015, 37(4): 953-965.

郑建常, 曲利, 曲均浩, 胡旭辉, 李冬梅. 乳山震群大小台网地震定位的对比研究[J]. 地震地质, 2015, 37(4): 953-965.

References

郭敬辉, 陈福坤, 张晓曼, 等. 2005. 苏鲁超高压带北部中生代岩浆侵入活动与同碰撞—碰撞后构造过程: 锆石U-Pb年代学［J］. 岩石学报, 21(4): 1281—1301.
GUO Jing-hui, CHEN Fu-kun, ZHANG Xiao-man, et al. 2005. Evolution of syn- to post-collisional magmatism from north Sulu UHP belt, eastern China: Zircon U-Pb geochronology ［J］. Acta Prtrologica Sinica, 21(4): 1281—1301(in Chinese).
郭敬辉, 翟明国, 叶凯, 等. 2002. 胶东海阳所高压变质基性岩的岩石化学和地球化学［J］. 中国科学(D辑), 32(5): 394—404.
GUO Jing-hui, ZHAI Ming-guo, YE Kai, et al. 2002. Petrochemistry and geochemistry of Haiyangsuo high pressure metamorphic rock in Jiaodong Peninsula ［J］. Science in China(Ser D), 32(5): 394—404(in Chinese).
胡芳芳, 范宏瑞, 沈昆, 等. 2005. 胶东乳山脉状金矿床成矿流体性质与演化［J］. 岩石学报, 21(5): 1329—1338.
HU Fang-fang, FAN Hong-rui, SHEN Kun, et al. 2005. Nature and evolution of ore-forming fluids in the Rushan lode gold deposit, Jiaodong Peninsula of eastern China ［J］. Acta Petrologica Sinica, 21(5): 1329—1338(in Chinese).
刘善宝. 2005. 山东乳山金青顶金矿田成矿规律及其成矿远景研究［D］: ［学位论文］. 西安: 长安大学.
LIU Shan-bao. 2005. The metailegenic regularity of the Jinqingding gold deposit field and ore prospecting in Rushan, Shandong Province ［D］. Master degree thesis. Chang'an University, Xi'an(in Chinese).
王世进, 王来明, 万渝生, 等. 2009. 鲁东地区侵入岩形成时代和期次划分: 锆石SHRIMP U-Pb年龄的证据［J］. 山东国土资源, 25(12): 8—20, 25.
WANG Shi-jin, WANG Lai-ming, WAN Yu-sheng, et al. 2009. Study on intrusive rocks forming period and stages division in Ludong area ［J］. Shandong Land and Resources, 25(12): 8—20, 25(in Chinese).
徐扬, 杨坤光, 李日辉, 等. 2013. 北苏鲁超高压变质带前寒武纪基底研究新进展［J］. 现代地质, 27(2): 248—259.
XU Yang, YANG Kun-guang, LI Ri-hui, et al. 2013. Main progresses in the study of Precambrian basement of the north Sulu ultra-high pressure metamorphic belt, eastern China ［J］. Geoscience, 27(2): 248—259(in Chinese).
闫俊岗, 王利兵, 谭青. 2013. 初始震源深度对双差地震定位深度的影响分析［J］. 大地测量与地球动力学, 33(增刊): 41—44.
YAN Jun-gang, WANG Li-bing, TAN Qing. 2013. Initial focal depth impact on depth of double difference earthquake relocation ［J］. Journal of Geodesy and Geodynamics, 33(suppl): 41—44(in Chinese).
杨喜安, 赵国春, 刘家军, 等. 2011. 胶东牟乳成矿带板块碰撞成矿作用及找矿方向［J］. 黄金, 32(2): 11—18.
YANG Xi-an, ZHAO Guo-chun, LIU Jia-jun, et al. 2011. Metallogenesis of plate collision and prospecting direction of the Muping-Rushan metallogenic belt, Jiaodong Peninsula ［J］. Gold, 32(2): 11—18(in Chinese).
翟明国, 郭敬辉, 王清晨, 等. 2000. 苏鲁变质带北部的岩石构造单元及结晶块体推覆构造［J］. 地质科学, 35(1): 16—26.
ZHAI Ming-guo, GUO Jing-hui, WANG Qing-chen, et al. 2000. Division of petrological-tectonic units in the northern Sulu ultra-high pressure zone: An example of thick-skin thrust of crystalline units ［J］. Scientia Geologica Sinica, 35(1): 16—26(in Chinese).
张华锋, 翟明国, 何中甫, 等. 2004. 胶东昆嵛山杂岩中高锶花岗岩地球化学成因及其意义［J］. 岩石学报, 20(3): 369—380.
ZHANG Hua-feng, ZHAI Ming-guo, HE Zhong-fu, et al. 2004. Petrogenesis and implications of the sodium-rich granites from the Kunyushan complex, eastern Shandong Province ［J］. Acta Petrologica Sinica, 20(3): 369—380(in Chinese).
郑建常, 李冬梅, 曲利, 等. 2014. 2013年乳山震群精定位研究［A］. 见: 2014年中国地球科学联合学术年会会刊. 北京.
ZHENG Jian-chang, LI Dong-mei, QU Li, et al. 2014. Accurate relocation of 2013 Rushan earthquake swarm ［A］. In: Proceedings of 2014 Annual Meeting of Chinese Union of Geosciences.
郑建常, 林眉, 王鹏, 等. 2015. CAP方法反演震源机制的误差分析: 以胶东半岛2次显著中等地震为例［J］. 地球物理学报, 58(2): 453—462.
ZHENG Jian-chang, LIN Mei, WANG Peng, et al. 2015. Error analysis for focal mechanisms from CAP method inversion: An example of 2 moderate earthquakes in Jiaodong Peninsula ［J］. Chinese J Geophys, 58(2): 453—462(in Chinese).
周起凤, 李胜荣, 陈海燕, 等. 2011. 胶东乳山英格庄金矿碲化物的发现及其意义［J］. 岩石学报, 27(6): 1847—1856.
ZHOU Qi-feng, LI Sheng-rong, CHEN Hai-yan, et al. 2011. Discovery and geological significance of telluride minerals in the Yinggezhuang gold deposit, Rushan, Jiaodong ［J］. Acta Petrologica Sinica, 27(6): 1847—1856(in Chinese).
Hainzl S. 2004. Seismicity patterns of earthquake swarms due to fluid intrusion and stress triggering ［J］. Geophys J Int, 159(3): 1090—1096. doi: 10.1111/j.1365-246X.2004.02463.x.
Waldhauser F, Ellsworth W L. 2000. A double-difference earthquake location algorithm: Method and application to the Northern Hayward Fault, California ［J］. Bull Seism Soc Amer, 90(6): 1353—1368.

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