利用高采样率数采实现地震波速变化高精度测量
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摘要
介质物理性质与应力状态的改变是导致地震波速变化的主要因素,通过高精度波速变化测量可推测地下介质发生的变化。然而,高精度波速变化测量对测量仪器提出了较高要求,波速变化的测量精度常常受到仪器的采样率、信噪比以及时间触发精度的影响。为实现高精度测量,设计一套由大功率稀土超磁致可重复震源和高采样率通用数采组成的观测系统,通过叠加的办法提高信噪比,利用增加采样率的方法提高时间触发精度。同时,使用近场数据进行校正,以消除仪器响应对波速变化的影响。实际观测表明,该系统能够明显减小走时测量误差,实现地震波速变化高精度测量。
Physical properties of the medium as well as its stress status change are the main factors that causes seismic velocity change,thus variations in the medium can be speculated by monitoring velocity change.However,precision of the measurement is usually affected by sample rate, SNR of the instruments and time triggered precision.With the purpose of realize high precision measurement,we designed a set of monitoring system,which includes a highpowered rare-earth giant magnetostrictive source and a general data-acquisition system with high sample rate.We used stacking to increase SNR,and enhanced the trigger precision by increasing the sample rate.Meanwhile,we used the near-field data for correction,so as to eliminate the instrument effects on seismic velocity change.The practical observation suggests that our system can obviously decrease time error,and realize high precision measurement of seismic velocity.
Physical properties of the medium as well as its stress status change are the main factors that causes seismic velocity change,thus variations in the medium can be speculated by monitoring velocity change.However,precision of the measurement is usually affected by sample rate, SNR of the instruments and time triggered precision.With the purpose of realize high precision measurement,we designed a set of monitoring system,which includes a highpowered rare-earth giant magnetostrictive source and a general data-acquisition system with high sample rate.We used stacking to increase SNR,and enhanced the trigger precision by increasing the sample rate.Meanwhile,we used the near-field data for correction,so as to eliminate the instrument effects on seismic velocity change.The practical observation suggests that our system can obviously decrease time error,and realize high precision measurement of seismic velocity.
引文
龙士国,马天朗.超磁震源声波CT仪的研制及其在工程无损评价中的应用//中国仪器仪表学会第九届青年学术会议中国仪器仪表学会第九届青年学术会议论文集[C].2007．
谭震,蒋洪明.数据采集中触发同步和精确定时的实现[J].自动化仪表,1998,19(5) :8-9,12．
王伟涛,王宝善,葛洪魁,等.利用主动震源检测汶川地震余震引起的浅层波速变化[J].中国地震,2009,25(3) :223-233．
张文毓.稀土磁致伸缩材料的应用[J].金属功能材料,2004,11(4) :42-46．
赵小贺,卢双苓,冯志军,等.洞体形变数字化观测干扰分析[J].地震地磁观测与研究,2009,30(4) :55-62．
Cespedes I,Huang Y,Ophir J,et al.Methods for estimation of sub-sample time delays of digitized echo signals[J].Ultrason Imag,1995,17:142-171．
De Fazio,T,K Aki and J Alba.Solid earth tide and observed change in the in situ seismic velocity[J].J Geophys Res,1973,78(8) :1 319-1 322．
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Liu H P,Sembera E D,Westerlund R E,et al.Tidal variation of seismic travel times in a Massachusetts granite quarry[J].Geophys Res Lett,1985,12(5) :243-246．
Nishimura T,Uchida N,Sato H,et al.Temporal changes of the crustal structure associated with the M 6． 1 earthquake on September 3,1998,and the volcanic activity of Mount Iwate,Japan[J].Geophys Res Lett,2000,27(2) :269-272．
Niu Fenglin.Preseismic velocity changes observed from active source monitoring at the Parkfield SAFOD drill site[J].Nature,2008,454:204-208．
O'Connell R,Budiansky B.Seismic velocities in dry and saturated cracked solids[J].J Geophys Res,1974,79(35) :5 412-5 426．
Pandolfi D,Bean C J,Saccorotti G.Coda wave interferometric detection of seismic velocity changes associated with the 1999 M 3． 6 event at Mt.Vesuvius[J].Geophys Res Lett,2006,33． L06306．
Reasenberg P,Aki K.A Precise,Continuous measurement of seismic velocity for monitoring in situ stress[J].J Geophys Res,1974,79(2) :399-406．
Rubinstein J L,Uchida N,Beroza G C.Seismic velocity reductions caused by the 2003 Tokachi-Oki earthquake[J].J Geophys Res,2007,112． B05315．
SawazakiKaoru,Haruo Sato,Hisashi Nakahara,et al.Time-Lapse Changes of Seismic Velocity in the Shallow Ground Caused by Strong Ground Motion Shock of the 2000 Western-Tottori Earthquake,Japan,as Revealed from Coda Deconvolution Analysis[J].Bulletin of the Seismological Society of America,2009,99(1) :352-366．
SilverPaul G,Thomas M,Daley,Fenglin Niu,Ernest L Majer.Active source monitoring of cross-well seismic travel time for stress-induced changes[J].Bulletin of Seismological Society of America,2007,97(1B):281-293．
SPECTRUM-Datasheet of the MI.31xx family[EB/OL].http://www.spectrum-gmbh.com/fileadmin/english/datasheets/mi31xx/mi31_datasheet_english.pdf.
Wang B,Zhu P,Chen Y,et al.Continuous subsurface velocity measurement with coda wave interferometry[J].J Geophys Res,2008:113．
Yamamura K,Sano O,Utada H,et al.Long-term observation of in situ seismic velocity and attenuation[J].J Geophys Res,2003:108．
Yukutakc H,Nakajima T,Doi K.In situ measurements of elastic wave velocity in a mine,and the effects of water and stress on their variation[J].Tectonophysics,1988,149(1-2) :165-175．
谭震,蒋洪明.数据采集中触发同步和精确定时的实现[J].自动化仪表,1998,19(5) :8-9,12．
王伟涛,王宝善,葛洪魁,等.利用主动震源检测汶川地震余震引起的浅层波速变化[J].中国地震,2009,25(3) :223-233．
张文毓.稀土磁致伸缩材料的应用[J].金属功能材料,2004,11(4) :42-46．
赵小贺,卢双苓,冯志军,等.洞体形变数字化观测干扰分析[J].地震地磁观测与研究,2009,30(4) :55-62．
Cespedes I,Huang Y,Ophir J,et al.Methods for estimation of sub-sample time delays of digitized echo signals[J].Ultrason Imag,1995,17:142-171．
De Fazio,T,K Aki and J Alba.Solid earth tide and observed change in the in situ seismic velocity[J].J Geophys Res,1973,78(8) :1 319-1 322．
DEWETRON_DATA-ACQUISITON-SOLUTIONS[EB/OL].http://download.dewetron.com/_media//files/products/catalog/dewetron_data-acquisition-solutions_de-b080201e.pdf.
Leary P,Malin P,Phinney R,et al.Systematic monitoring of millisecond travel time variations Near Palmdale,California[J].J Geophys Res,1979,84(B2) :659-666．
Liu H P,Sembera E D,Westerlund R E,et al.Tidal variation of seismic travel times in a Massachusetts granite quarry[J].Geophys Res Lett,1985,12(5) :243-246．
Nishimura T,Uchida N,Sato H,et al.Temporal changes of the crustal structure associated with the M 6． 1 earthquake on September 3,1998,and the volcanic activity of Mount Iwate,Japan[J].Geophys Res Lett,2000,27(2) :269-272．
Niu Fenglin.Preseismic velocity changes observed from active source monitoring at the Parkfield SAFOD drill site[J].Nature,2008,454:204-208．
O'Connell R,Budiansky B.Seismic velocities in dry and saturated cracked solids[J].J Geophys Res,1974,79(35) :5 412-5 426．
Pandolfi D,Bean C J,Saccorotti G.Coda wave interferometric detection of seismic velocity changes associated with the 1999 M 3． 6 event at Mt.Vesuvius[J].Geophys Res Lett,2006,33． L06306．
Reasenberg P,Aki K.A Precise,Continuous measurement of seismic velocity for monitoring in situ stress[J].J Geophys Res,1974,79(2) :399-406．
Rubinstein J L,Uchida N,Beroza G C.Seismic velocity reductions caused by the 2003 Tokachi-Oki earthquake[J].J Geophys Res,2007,112． B05315．
SawazakiKaoru,Haruo Sato,Hisashi Nakahara,et al.Time-Lapse Changes of Seismic Velocity in the Shallow Ground Caused by Strong Ground Motion Shock of the 2000 Western-Tottori Earthquake,Japan,as Revealed from Coda Deconvolution Analysis[J].Bulletin of the Seismological Society of America,2009,99(1) :352-366．
SilverPaul G,Thomas M,Daley,Fenglin Niu,Ernest L Majer.Active source monitoring of cross-well seismic travel time for stress-induced changes[J].Bulletin of Seismological Society of America,2007,97(1B):281-293．
SPECTRUM-Datasheet of the MI.31xx family[EB/OL].http://www.spectrum-gmbh.com/fileadmin/english/datasheets/mi31xx/mi31_datasheet_english.pdf.
Wang B,Zhu P,Chen Y,et al.Continuous subsurface velocity measurement with coda wave interferometry[J].J Geophys Res,2008:113．
Yamamura K,Sano O,Utada H,et al.Long-term observation of in situ seismic velocity and attenuation[J].J Geophys Res,2003:108．
Yukutakc H,Nakajima T,Doi K.In situ measurements of elastic wave velocity in a mine,and the effects of water and stress on their variation[J].Tectonophysics,1988,149(1-2) :165-175．
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