芦山M_S7.0地震前远、近场形变时空演化特征研究
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摘要
应用芦山MS7.0地震震中附近跨断层及连续形变观测资料,分析了芦山地震前不同阶段地形变变化的特点,讨论了震中附近区域异常时空演化过程.结果表明:①自2013年1月起,沿鲜水河断裂带一些跨断层基线观测到显著的加速转折变化,沿安宁河、则木河断裂带个别场地的跨断层水准基线,2010年以来出现的巨幅异常等是突出的场兆变化;沿龙门山断裂带一些水准观测在汶川MS8.0地震后持续的调整变化具有近震源区变形特征.②鲜水河、龙门山和安宁河3条主要断裂围成的三叉口地区,地倾斜、应变、重力及断层水准和蠕变观测临震前均未有显著的异常变化,GPS水平、垂直位移年速率最小,该地区是形变变化或形变异常分布的"空区".③在对近场与远场多种连续形变数据通过傅里叶变换提取年周期成分后发现,临震前2—3年近震源区域的地倾斜、重力年变化幅度不是增大,而是减小.芦山MS7.0地震前观测到的形变前兆现象特征与汶川MS8.0地震等震前的前兆现象较为接近.因此,芦山地震前近震源区及外围形变异常分布特征不是个别的现象.
This paper analyzes and discusses the spatio-temporal evolutionary characteristics of deformation prior to the Lushan MS7.0 earthquake,based on the data of cross fault and continuous deformation measurements near the epicenter of the earthquake.The results show that:① the cross fault baseline length has been significant acceleration-turning at some cross-fault sites along the Xianshuihe fault since January of 2013,and some anomalies of leveling and baseline lengths recorded at individual sites along Anninghe and Zemuhe faults are the field precursors.Small adjustment of most of the leveling cross the Longmenshan fault presented the characteristic of source precursors.②In the cross connected area of the Xianshuihe,Longmenshan and Anninghe faults,no significant anomalies were recorded by means of continuous deformation(tilt,strain,gravity),fault leveling,and creep observation.Moreover,the GPS horizontal and vertical velocities nearby the source are smaller than the outer region,so there is a concept of Weak Area,where no significant changes in deformation or no anomalies.③ The annual amplitude of tilt and gravity in the near-field,extracted by the Fourier transform,is reduced 2—3 years prior to the event,which is our newly understanding about the earthquake precursors.The results mentioned above indicate that the precursory phenomena before the Lushan MS7.0 earthquake,observed by deformation measurements,are similar to those before Wenchuan MS8.0 and so on,so it is not individual.
This paper analyzes and discusses the spatio-temporal evolutionary characteristics of deformation prior to the Lushan MS7.0 earthquake,based on the data of cross fault and continuous deformation measurements near the epicenter of the earthquake.The results show that:① the cross fault baseline length has been significant acceleration-turning at some cross-fault sites along the Xianshuihe fault since January of 2013,and some anomalies of leveling and baseline lengths recorded at individual sites along Anninghe and Zemuhe faults are the field precursors.Small adjustment of most of the leveling cross the Longmenshan fault presented the characteristic of source precursors.②In the cross connected area of the Xianshuihe,Longmenshan and Anninghe faults,no significant anomalies were recorded by means of continuous deformation(tilt,strain,gravity),fault leveling,and creep observation.Moreover,the GPS horizontal and vertical velocities nearby the source are smaller than the outer region,so there is a concept of Weak Area,where no significant changes in deformation or no anomalies.③ The annual amplitude of tilt and gravity in the near-field,extracted by the Fourier transform,is reduced 2—3 years prior to the event,which is our newly understanding about the earthquake precursors.The results mentioned above indicate that the precursory phenomena before the Lushan MS7.0 earthquake,observed by deformation measurements,are similar to those before Wenchuan MS8.0 and so on,so it is not individual.
引文
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朱令人,王海涛,白超英,周仕勇,龚宇清.1990.澜沧—耿马7.6级地震前中小地震活动信息熵和分维的研究[J].内陆地震,4(4):310--317.
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Bilham R.2005.Co-seismic strain and the transition to surface afterslip recorded by creep-meters near the 2004Parkfield epicenter[J].Seism Res Lett,76(1):49--57.
Das S,Scholz C H.1981.Theory of time-dependent rupture in the Earth[J].J Geophys Res,86(B7):6039--6051.
Dubrovskiy V A,Sergeev V N.2006.Short-and medium-term earthquake precursors as evidence of the sliding instability along faults[J].Physics of the Solid Earth,42(10):802--808.
Johnston M J S,Linde A T,Gladwin M T.1990.Near-field high precision strain prior to the October 18,1989Loma Prieta ML7.1earthquake[J].Geophys Res Lett,17:1777--1780.
Johnston M J S,Mortensen C E.1974.Tilt precursors before earthquakes on the San Andreas fault,California[J].Science,186:1031--1034.
Linde T,Gladwin M T,Johnston M J S.1992.The Loma Prieta earthquake,1989and earth strain tidal amplitudes:An unsuccessful search for associated changes[J].Geophys Res Lett,19(3):317--320.
Mjachkin V I,Brace W F,Sobolev G A,Dieterich J H.1975.Two models for earthquake forerunners[J].Pure Appl Geophys,113(1):169--181.
McHugh S,Johnston M J S.1978.Dislocation modeling of creep-related tilt changes[J].Bull Seismol Soc Am,68:155--168.
Mogi K.1985.Temporal variation of crustal deformation during the days preceding a thrust-type great earthquake:The1944Tonankai earthquake of magnitude 8.1,Japan[J].Pure Appl Geophys,122(6):765--780.
Nur A.1972.Dilatancy,pore fluids and premonitory variations of tS/tP travel times[J].Bull Seismol Soc Am,62(5):1217--1222.
Rikitake T.1975.Dilatancy model and empirical formulas for an earthquake area[J].Pure Appl Geophys,113(1):141--146.
Rummel F,Alheid H J,Frohn C.1978.Dilatancy and fracture induced velocity changes in rock and their relation to frictional sliding[J].Pure Appl Geophys,116:743--764.
Takemoto S.1991.Some problems on detection of earthquake precursors by means of continuous monitoring of crustal strains and tilts[J].J Geophys Res,96(B6):10377--10390.
牛安福.2003.地倾斜变化的突变性及与地震关系的研究[J].地震学报,25(4):441--445.
牛安福.2005.地震短期、短临预测面临的“最后一分钟”[J].国际地震动态,(2):29--31.
牛安福,张凌空,闫伟,吉平.2012.汶川地震近震源区地形变短期前兆现象的解析[J].地震,32(2):52--63.
牛安福,张凌空,闫伟,贾晓东,李晓帆.2009.汶川地震前南北地震带中北段地形变变化特征的研究[J].地震,29(1):100--107.
牛安福,张雁滨,柯丽君,刘祖荫,郑文衡.1999.地震前地壳形变异常分布的非均匀性特征[J].地震,19(2):149--154.
王海涛,杨马陵.1990.地震前兆系统信息熵的初步研究[J].中国地震,6(2):10--14.
吴翼麟.1990.定点形变前兆预报地震的观测技术与分析方法[J].地震,(5):33--45.
周硕愚,施顺英,帅平.1997.唐山地震前后地壳形变场的时空分布、演化特征与机理研究[J].地震学报,19(6):559--565.
朱传镇.1989.应用熵的原理推进地震活动定量化研究[J].地震,12(1):75--76.
朱令人,王海涛,白超英,周仕勇,龚宇清.1990.澜沧—耿马7.6级地震前中小地震活动信息熵和分维的研究[J].内陆地震,4(4):310--317.
Amoruso A,Crescentini L.2010.Limits on earthquake nucleation and other pre-seismic phenomena from continuous strain in the near field of the 2009 L′Aquila earthquake[J].Geophys Res Lett,37:L10307,doi:10.1029/2010GL043308,2010.
Bilham R.2005.Co-seismic strain and the transition to surface afterslip recorded by creep-meters near the 2004Parkfield epicenter[J].Seism Res Lett,76(1):49--57.
Das S,Scholz C H.1981.Theory of time-dependent rupture in the Earth[J].J Geophys Res,86(B7):6039--6051.
Dubrovskiy V A,Sergeev V N.2006.Short-and medium-term earthquake precursors as evidence of the sliding instability along faults[J].Physics of the Solid Earth,42(10):802--808.
Johnston M J S,Linde A T,Gladwin M T.1990.Near-field high precision strain prior to the October 18,1989Loma Prieta ML7.1earthquake[J].Geophys Res Lett,17:1777--1780.
Johnston M J S,Mortensen C E.1974.Tilt precursors before earthquakes on the San Andreas fault,California[J].Science,186:1031--1034.
Linde T,Gladwin M T,Johnston M J S.1992.The Loma Prieta earthquake,1989and earth strain tidal amplitudes:An unsuccessful search for associated changes[J].Geophys Res Lett,19(3):317--320.
Mjachkin V I,Brace W F,Sobolev G A,Dieterich J H.1975.Two models for earthquake forerunners[J].Pure Appl Geophys,113(1):169--181.
McHugh S,Johnston M J S.1978.Dislocation modeling of creep-related tilt changes[J].Bull Seismol Soc Am,68:155--168.
Mogi K.1985.Temporal variation of crustal deformation during the days preceding a thrust-type great earthquake:The1944Tonankai earthquake of magnitude 8.1,Japan[J].Pure Appl Geophys,122(6):765--780.
Nur A.1972.Dilatancy,pore fluids and premonitory variations of tS/tP travel times[J].Bull Seismol Soc Am,62(5):1217--1222.
Rikitake T.1975.Dilatancy model and empirical formulas for an earthquake area[J].Pure Appl Geophys,113(1):141--146.
Rummel F,Alheid H J,Frohn C.1978.Dilatancy and fracture induced velocity changes in rock and their relation to frictional sliding[J].Pure Appl Geophys,116:743--764.
Takemoto S.1991.Some problems on detection of earthquake precursors by means of continuous monitoring of crustal strains and tilts[J].J Geophys Res,96(B6):10377--10390.
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