云南velocity地震成像揭示地下结构对破裂滑动分布的控制关系

1、张海江地震成像揭示地下结构对地震破裂滑动分布的控制关系邮件： 网址： What controls rupture direction?What controls slip distribution?Is barrier strong or weak?张勇 et al., 2015裴顺平裴顺平, 2016, 大理大理Bakun and Lindh, 1985, ScienceIn 1984, Bakun and McEvilly noticed that Parkfield had experienceda M6 earthquake an average of once every 22 ye

2、arsM6 Earthquakes in Parkfield1840186018801900192019401960198020002020012345678EarthquakeDateand they predicted the next one between 1983 and 1993.Bakun and Lindh, 1985, ScienceIn 1984, Bakun and McEvilly noticed that Parkfield had experienceda M6 earthquake an average of once every 22 yearsIt did n

3、ot happen until September 28, 2004Ji Chen UCSBLangbein et al., 2005More surprises:More surprises:The 2004 The 2004 earthquake is earthquake is located around located around Gold Hill, NOT Gold Hill, NOT Middle Mountain.Middle Mountain.The 2004 The 2004 earthquake earthquake ruptures to ruptures to n

4、orthwest, while northwest, while the 1966 the 1966 earthquake earthquake ruptures to ruptures to southeast.southeast.What controls rupture direction?For a bi-material fault model, the rupture direction should be in the slip direction of the “softer” rock.Andrews and Ben-Zion, 1997Ben-Zion and Andrew

5、s, 1998 What controls rupture direction?For a bi-material fault model, the rupture direction should be in the slip direction of the “softer” rock.Andrews and Ben-Zion, 1997Ben-Zion and Andrews, 1998 What controls rupture direction?200520062006Association between 2004 slip patch and high-Vp body on n

6、ortheast sideof the San Andreas faultModified from Thurber and Zhang et al. (2006)NWNESESWNew 2004 Parkfield earthquake rupture model:Ma et al. (2007)Rupture constrained to lie within aftershock streaksMa et al. (2007)Comparison to high-resolution tomography model with wavelet-tomoDD:New 2004 Parkfi

7、eld earthquake rupture model:Rupture constrained to lie within aftershock streaksFang &Zhang, 2014Some observations: Parkfield rupture models consistently show two slip patches, small one to the SE and large one to the NW Between two Parkfield earthquakes, there exists a high-Vp body (limestone

8、and greenstone)What controls rupture direction?What controls slip distribution?What controls rupture direction?What controls slip distribution?Controlled by fault material/structure changes along the fault? Rate- and state-variable friction lawFriction terma-b0 UnstableVelocity weakeninga-b0 StableV

9、elocity strengtheningScholz, 1998, Naturea, b: material parameters“the gamut of earthquake phenomena all appear as manifestations of the richness of this friction law”Rate- and state-variable friction lawFriction termScholz, 1998, Naturea, b: material parametersElastic-brittle deformation to crystal

10、 plasticitya-b from negative to positive Aki, 1984, JGR Seno, 2003, EPSAsperities: a-Asperities: a-b0b0Barriers: a-b0Fault plane: could be defined as a broad weak zone with a locally strong part (asperity)Shibazaki and Matsuura, 1992, GRL 陈晓非， 2016， 大理For materials showing plastic Deformationa-b0Lar

11、ge DcMarone, 1998What controls rupture direction?What controls slip distribution?Controlled by fault material/structure changes along the fault! AsperityBarrierBarrierMore examples2008 Mw6.0 earthquake along the Gofar transform fault, east Pacific rise2008 Wenchuan and 2013 Lushan earthquakes along

12、the Longmenshan faultFroment et al., 20142D velocity inversion2D velocity inversionVp/Vs Vp/Vs from 3D from 3D inversioinversion n博士生：郭浩2008 Mw6.0 earthquake is located around the boundary of low Vp/Vs (strong) and high Vp/Vs (weak) anomalies.Froment et al., 20142D velocity inversion2D velocity inve

13、rsion衰减（Qs）模型博士生：胡景2008 Mw6.0 earthquake is located around the boundary of low Q (strong) and high Q (weak) anomalies.Modified from Froment et al., 2014，JGRLow Vp/VsLow QHigh Vp/Vs High QHigh Vp/Vs High QAsperityBarrierBarrierMore examples2008 Mw6.0 earthquake along the Gofar transform fault, east P

14、acific rise2008 Wenchuan and 2013 Lushan earthquakes along the Longmenshan fault王为民等，2008，地球物理学报Relationship between velocity and rupture for Wenchuan M 8.0 EarthquakeVpVsDisplacementNishimura & Yagi (2008)Vp and Vs models are obtained by DD tomography (Pei, Su, and Zhang et al., Tectonophysics,

15、 2010 )SWNEVp/Vs2013年4月20日芦山地震2008年汶川地震和2013年龙门山地震之间存在余震空白区两次地震都没有在空白区产生破裂滑动Hao et al., 2013, GRLPgPg波速度分布波速度分布余震的空白区可能是一个塑性变形区，因此大地震发生的可能性可能不高。Geodynamic ModelGeodynamic ModelPei & Zhang et al., 2014, Scientific Reports 不同周期下面波相速度的分布体波走时曲线Tomography method: Joint inversion of body wave arrivals

16、 time and surface wave dispersion dataZhang et al., 2014, Pure & Applied Geophysics;Fang, Zhang, Yao et al., 2016, JGR 研究生：高丽娜Separately inverted VpSeparately inverted VsJointly inverted Vs Along the Longmenshan fault, there are three high velocity bodies (asperities of 2008 Wenchuan earthquake

17、and 2013 Lushan earthquake, respectively). Along the Longmenshan fault, there are two low velocity bodies (one acting as barriers for Wenchuan and Lushan earthquakes). Large earthquakes (M5) are generally located around the edge of high velocity bodies.2013 芦山地震断层滑动分布模型Hao et al., 2013, GRL 在地表几乎没有观

18、测到破裂（徐锡伟等，2013）郑勇等布置临时余震监测台网29 个短周期台站主震发生大约一周后开始布置地震综合成像方法多网格地震速度成像（5km、2km、1km） （硕士生张欣）Vp, Vs, Vp/Vs地震定位基于速度结构约束的地震衰减成像（硕士生张欣）Qp, Qs地震横波分裂各向异性成像（博士生刘影）各向异性强度不同网格的棋盘分辨率测试（以深度9公里为例）5km-grid2km-grid1km-grid速度模型（平行于断层）VpVs在大约8公里深度，速度变化显著。浅部：低速深部：高速地震主要发生在高速异常区域和Li et al. (2013, GJI)结果类似。VpVsDDEEFFAlong

19、 the main thrust fault at shallow region, there is a velocity contrast from NW to SE. 速度模型（垂直于断层）平行于断层走向的VpVs剖面垂直于断层走向的VpVs剖面快波极化方向分布存在双个方向Liu & Zhang et al. (2015)G-cubed横波分裂分析各向异性强度Strong anisotropy above the fault plane delineated by aftershocksLikely caused by shear fabric along the fault pl

20、ane3D shear wave splitting tomography (Zhang et al., 2007, GRL)Liu&Zhang et al., (2015, G-cubed)浅层介质弱：低速高泊松比高衰减应力不容易积累不易发生脆性断裂深层介质强：高速低泊松比低衰减应力容易积累容易发生脆性断裂Vp/VsQs浅部异常高的各向异性也意味着浅部裂缝发达Shear-wave splitting delay timesAnisotropy percentage along the faultDelay times are up to 0.4 seconds, compared to 0.1 seconds in other fault zones. The anisotropy percentage can be up to 5%. The shallow part is highly anisotropic and fractured. Comparison of velocity and slip modelsShallow part is weak: low velocity, high Vp/Vs, low slipDeeper part is strong: high velocity, low