地震研究

通过收集芦山地震主震的远震波形记录,利用pP深度震相的动校正叠加法对主震的震源深度进行了确定,不同窗长的计算结果显示该地震震源深度在(16±1)km处,与目前主流结果(14～18 km)一致; 同时,利用“区域深度震相建模”(Regional Depth Phase Modeling,RDPM)方法对4次M_S4.0以上强余震进行了震源深度的确定。通过对波形的比对,选择LTA台和PmP-sPmP震相对。为确保结果的可靠性,使用远震接收函数的H-k叠加结果修改了初始速度模型的莫霍面深度及波速比,并使用CAP方法计算了这些事件的震源机制解。结果显示,由RDPM得到的震源深度与利用区域直达波震相获得的精确定位结果几乎一致; 4个事件中有3个的深度范围与CAP的结果相近,有2个与台网快报相差无几。事实证明,利用远震深度震相和区域深度震相都能对震源深度有很好的约束,对于台站稀疏的地区来说,深度震相提供了一种相对准确的震源深度确认途径。

Firstly,the teleseismic waveforms of the Lushan main shock were colleted,and the focal depth was determined by using the dynamic-correction stacking method of the pP depth phase,the calculation results of different window size show that the focal depth of the main shock is(16±1)km and is consistent with the current mainstream results(14～18)km. In addition,the focal depths of four M_S≥4.0 strong aftershocks were determined by the “Regional Depth Phase Modeling”(RDPM). Through the waveform comparison,the LTA Station and the phase pair of PmP-sPmP were chose. To ensure the reliability of the results,we revised the depth of Moho and the V_p/V_s in the initial velocity model by using the H-k stacking from teleseismic receiver funtions of LTA station and the focal mechanism solutions by CAP method. The results show that the focal depths which is calculated by the RDPM and the precision location obtained by the regional direct phase are almost identical. The focal depth range of three events from four events is similar with that of the CAP method,and the focal depth range of two events is almost the same with the results of network express. The facts prove that teleseismic or regional depth phase both have the good constrain on the focal depth. For the region of sparse stations,the depth phases provide a relatively accurate way to confirm the focal depth.

引言
1 研究方法
2 数据处理及结果分析
3 结论和讨论

图1 主震深度计算中所使用的远震台站分布(a)和波形记录(b)<br/>Fig.1 Distribution of the stations(a)and waveforms(b)used in the focal depth calculation of main shock

图1 主震深度计算中所使用的远震台站分布(a)和波形记录(b)
Fig.1 Distribution of the stations(a)and waveforms(b)used in the focal depth calculation of main shock

图2 不同震源深度的pP震相截取窗在不同震中距台站记录波形(绝对值)上的位置<br/>Fig.2 The location of pP phase intercepted windows (lightgray portion,window size are 0.6 s)on waveforms recorded by station in different epicentral distance (absolute value)at different focal depth

图2 不同震源深度的pP震相截取窗在不同震中距台站记录波形(绝对值)上的位置
Fig.2 The location of pP phase intercepted windows (lightgray portion,window size are 0.6 s)on waveforms recorded by station in different epicentral distance (absolute value)at different focal depth

图3 不同时间窗长芦山地震pP震相的动校正叠加结果(图中的15.8 km为窗长为0.4 s时峰值所对应的震源深度)<br/>Fig.3 The pP phase dynamic-correction stacking results for the Lushan main shock using different window size(15.8 km in the figure is the focal depth corresponding to the peak

图3 不同时间窗长芦山地震pP震相的动校正叠加结果(图中的15.8 km为窗长为0.4 s时峰值所对应的震源深度)
Fig.3 The pP phase dynamic-correction stacking results for the Lushan main shock using different window size(15.8 km in the figure is the focal depth corresponding to the peak

表1 计算深度震相所使用的地震事件<br/>Tab.1 The earthquake events used in the depth phase calculation

表1 计算深度震相所使用的地震事件
Tab.1 The earthquake events used in the depth phase calculation

图4 高原台站LTA与盆地台站YTI、AYU记录到的同一事件的波形对比(地震为表1中的事件1,蓝色圆圈为芦山地震序列位置)<br/>Fig.4 Waveform comparision of the same event between LTA plateau staion and YTI,AYU basin stations (earthquake is the event 1 in tabel 1,the blue circles are the location of the Lushan sequence)

图4 高原台站LTA与盆地台站YTI、AYU记录到的同一事件的波形对比(地震为表1中的事件1,蓝色圆圈为芦山地震序列位置)
Fig.4 Waveform comparision of the same event between LTA plateau staion and YTI,AYU basin stations (earthquake is the event 1 in tabel 1,the blue circles are the location of the Lushan sequence)

图5 PmP和sPmP的射线路径(据Ma,Eaton,2011)<br/>Fig.5 The ray paths of PmP and sPmP phases(according to Ma,Eaton,2011)

图5 PmP和sPmP的射线路径(据Ma,Eaton,2011)
Fig.5 The ray paths of PmP and sPmP phases(according to Ma,Eaton,2011)

图6 LTA台的远震接收函数H-k叠加结果<br/>Fig.6 The H-k stacking result of teleseismic receiver funtions of LTA station

图6 LTA台的远震接收函数H-k叠加结果
Fig.6 The H-k stacking result of teleseismic receiver funtions of LTA station

图7 表1中4个事件不同震源深度的理论地震图(实线)和实际地震图(虚线)<br/>及PmP和sPmP震相的位置(a～d分别对应表1中的1～4号事件)<br/>Fig.7 The synthetic seismograms(solid line)and observed seismograms(dot line)and the location of the PmP and sPmP of 4 events in different focal depth in tab. 1(a～d corresponding to the No.1～4 events respectively in tab.1)

图7 表1中4个事件不同震源深度的理论地震图(实线)和实际地震图(虚线)
及PmP和sPmP震相的位置(a～d分别对应表1中的1～4号事件)
Fig.7 The synthetic seismograms(solid line)and observed seismograms(dot line)and the location of the PmP and sPmP of 4 events in different focal depth in tab. 1(a～d corresponding to the No.1～4 events respectively in tab.1)

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备注

引言

1 研究方法

2 数据处理及结果分析

3 结论和讨论

期刊信息