{"title":"Preliminary Results of the Seismicity Monitoring Experiment around the 2019 Mw5.4 Earthquake Epicenter in the Central South China Sea Basin","authors":"Wenfei Gong, Aiguo Ruan, Xiongwei Niu, Zhenjie Wang, Pingchuan Tan, Xiaodong Wei, Wei Wang, Zhengyi Tong, Liqun Cheng, Fansheng Kong, Shaoping Lu, Jianke Fan, Weiwei Ding, Jinyao Gao, Chunguo Yang, Jiabiao Li","doi":"10.1007/s12583-021-1604-y","DOIUrl":null,"url":null,"abstract":"<p>On September 5, 2019, a moderate earthquake of Mw5.4 unexpectedly occurred in the apparently quiescent central basin of the South China Sea. We immediately carried out a seismicity monitoring experiment around the epicenter by using broadband ocean bottom seismometers (OBS) for the following three scientific targets. The first is knowing the earthquake seismogenic mechanism, fault structure and further development. The second is finding the role of the residual spreading ridge playing in earthquake processes and further revealing the deep structures of the ridge directional turning area. The third is confirming the existence and significance of the so called “Zhongnan fault”. This paper reports the preliminary results of the first phase experiment. Five OBSs were deployed for seismicity monitoring with a duration of 288 days, but only three were recovered. Micro-earthquakes were firstly detected by an automatic seismic phase picking algorithm and then were verified by analyzing their seismic phases and time-frequency characteristics in detail. A total of 21, 68 and 89 micro-earthquakes were picked out from the three OBSs respectively within the distance of 30 km. The dominant frequency of these micro-earthquakes is 12–15 Hz, indicating tectonic fracturing. During the first two months after the mainshock the seismicity was relatively stronger, and micro-earthquakes were still occurring occasionally till the end of observation, indicating the epicenter area is active. We used Match&Locate method to locate 57 micro-earthquakes preliminarily. Their spatial distribution shows that the seismicity is developed mainly along the NE direction roughly parallel to the residual ridge with depth variations between 10–20 km.</p>","PeriodicalId":15607,"journal":{"name":"Journal of Earth Science","volume":"291 1","pages":""},"PeriodicalIF":4.1000,"publicationDate":"2024-02-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Journal of Earth Science","FirstCategoryId":"89","ListUrlMain":"https://doi.org/10.1007/s12583-021-1604-y","RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"GEOSCIENCES, MULTIDISCIPLINARY","Score":null,"Total":0}
引用次数: 0
Abstract
On September 5, 2019, a moderate earthquake of Mw5.4 unexpectedly occurred in the apparently quiescent central basin of the South China Sea. We immediately carried out a seismicity monitoring experiment around the epicenter by using broadband ocean bottom seismometers (OBS) for the following three scientific targets. The first is knowing the earthquake seismogenic mechanism, fault structure and further development. The second is finding the role of the residual spreading ridge playing in earthquake processes and further revealing the deep structures of the ridge directional turning area. The third is confirming the existence and significance of the so called “Zhongnan fault”. This paper reports the preliminary results of the first phase experiment. Five OBSs were deployed for seismicity monitoring with a duration of 288 days, but only three were recovered. Micro-earthquakes were firstly detected by an automatic seismic phase picking algorithm and then were verified by analyzing their seismic phases and time-frequency characteristics in detail. A total of 21, 68 and 89 micro-earthquakes were picked out from the three OBSs respectively within the distance of 30 km. The dominant frequency of these micro-earthquakes is 12–15 Hz, indicating tectonic fracturing. During the first two months after the mainshock the seismicity was relatively stronger, and micro-earthquakes were still occurring occasionally till the end of observation, indicating the epicenter area is active. We used Match&Locate method to locate 57 micro-earthquakes preliminarily. Their spatial distribution shows that the seismicity is developed mainly along the NE direction roughly parallel to the residual ridge with depth variations between 10–20 km.
期刊介绍:
Journal of Earth Science (previously known as Journal of China University of Geosciences), issued bimonthly through China University of Geosciences, covers all branches of geology and related technology in the exploration and utilization of earth resources. Founded in 1990 as the Journal of China University of Geosciences, this publication is expanding its breadth of coverage to an international scope. Coverage includes such topics as geology, petrology, mineralogy, ore deposit geology, tectonics, paleontology, stratigraphy, sedimentology, geochemistry, geophysics and environmental sciences.
Articles published in recent issues include Tectonics in the Northwestern West Philippine Basin; Creep Damage Characteristics of Soft Rock under Disturbance Loads; Simplicial Indicator Kriging; Tephra Discovered in High Resolution Peat Sediment and Its Indication to Climatic Event.
The journal offers discussion of new theories, methods and discoveries; reports on recent achievements in the geosciences; and timely reviews of selected subjects.