琼中地震台重力仪记录同震响应特征分析

2013年2月6-8日圣克鲁斯群岛发生6次强震,琼中地震台的重力仪记录都有同震响应出现。本文从重力仪记录的面波的延迟时间、最大变形幅度、同震持续时间3个方面研究了6次强震的同震响应特征。

Analysis of the Characteristics of the Coseismic Response of the Gravity Instrument at the Qiongzhong Seismostation

Far-field seismic-wave-induced fluctuation of water levels was first recorded in deep wells in Italy in 1899,and,since then,seismologists and hydrogeologists all over the world have been studying this phenomenon.Since the loading of the coseismic response has wide regional characteristics,its features are easily recognized.Today,since no breakthrough progress has been made in the study of seismic precursor mechanisms,the study of coseismic response is of critical importance for the understanding of earthquakes and their precursors.Interim characteristics of the wave,wave characteristics,and earthquake preparation process using the whole point semidiurnal tidal observation data can represent the solid earth tides well,but not the pre-earthquake short-term fluctuations due to the large-scale sampling rate increase,suggesting that the use of digital deformation observation data is preferable.Since short-cycle fluctuation and jumping occur before the earthquake,precursor short-impending information and co-seismic deformation information of global earthquakes are essential.In February 2013,six earthquakes occurred in the Santa Cruz Islands,and there was a coseismic response of the gravimeter at Qiongzhong.The coseismic response characteristics in three aspects of delay time of surface wave,the greatest deformation range and co-seismic duration were researched.In this paper,we study 6earthquakes in the Santa Cruz Islands on February 6,2013.Before an earthquake,the gravity instrument observation curve is smooth;the observational curve of the gravimeter at the Qiongzhong seismostation on Feb.6,2013denotes a strong earthquake(MS7.5),which shows a pulse-shape at the onset of pulsation,recorded at 09:22. (Beijing time)The response curve of the gravimeter reaches a low value by 09:44and rises gradually to a peak at 09:46,before returning to the original level,lasting a total of 42minutes.The result shows that the time delay of the surface wave is the same in earthquakes originating at thesame place.The duration of the coseismic response is related to the resolution ratio of the observation instrument;the amplitude of the coseismic response is positive correlated with the magnitude of the earthquake.The coseismic responses are mostly high-frequency impulses caused by surface waves,some of which had long periods.The strain-step changes and wave motions were caused by the arrival of the corresponding surface waves.The shape and size of the step changes and the response time recorded by different instruments were different;this difference is probably a reflection of different instrument properties,such as sensitivity and frequency response.The result may help us reach a better understanding of the performance of digital observation instruments,providing us a way to study the short-impending anomaly prior to earthquake.Further analysis and studies on focal mechanism of the earthquake is necessary to better understand the characteristics of gravimeter records for distant and strong earthquakes.