Coseismic displacement field and slip model derived from near-source strong motion records of MW7.0 Kumamoto, Japan, earthquake
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摘要: 利用2016年4月16日日本熊本MW7.0地震震中周围94个近场强震动台的观测资料和新近改进的强震经验基线校正方法SMBLOC，尝试解算并绘制了一个内陆M7左右走滑型地震的同震位移场全貌，并反演了其震源滑动模型.与日本国土地理院(GSI)公布的该地震57个GPS同震位移结果的比较显示，两种完全不同资料、不同解算方法给出的水平同震位移场的最大幅值均为100 cm左右，均呈右旋走滑为主兼具部分正断分量的震源机制.强震最大水平和垂直永久位移分别为104.5 cm和58.0 cm, 分别出现在震中东北侧的KMMH162台和KMM005台.两种资料单独以及联合反演的震源滑动模型均表明，此次地震为北东侧破裂为主并呈双事件特征，且主要滑动均不在初始破裂点附近, 而是集中于第二次事件周围，即距离初始破裂点东北侧约20 km处的走向长约40 km、倾向宽约20 km的范围内.基于强震和GPS模型所得的最大滑动量分别为5.10 m和5.87 m，量级一致，反演矩震级均为MW7.1左右；主破裂区近地表滑动量比野外调查结果略微偏大，可能与数值效应有关.此外，还利用不同方法得到的解算结果比较了熊本地震特有的12组台间距在3 km以内的GPS-强震台站对各自的三分量同震位移，其结果表明对于M7左右的地震而言，SMBLOC方法解算同震位移时方向和幅值的可靠性下限约为2 cm.
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关键词:
- 内陆走滑型地震 /
- 自动经验基线校正 /
- 同震位移 /
- 滑动模型 /
- 2016年4月16日熊本MW7.0地震
Abstract: Near-source coseismic displacement field of the 16 April 2016 MW7.0 Kumamoto, Japan, earthquake is estimated from 94 digital strong motion records after correction for their baseline errors using an improved empirical method SMBLOG, and compared with that from 57 GPS observations published by Geospatial Information Authority of Japan (GSI). Furthermore, three slip models of the earthquake are inverted from the displacement data of the GPS, strong motion and their combination, suggesting the results are in good agreement. The three models all show that the earthquake is dominated by the right-lateral strike-slip mechanism (also a few normal-fault dislocations). The maximum horizontal and vertical coseismic displacements reached 104.5 cm and 58.0 cm, and occurred at the stations KMMH162 and KMM005, respectively. The fault slips are mainly distributed around the second event (about 20 km northeastward from epicenter) and in an area of about 40 km along the strike and 20 km along the dip. The moment magnitude is estimated to be MW7.1, and the peak slip is about 5.10 m for strong motion data and 5.87 m for GPS. The surface rupture should be obvious. Moreover, the comparison of the three-component coseismic displacements derived from 12 GPS-strong motion station-pairs with interval less than 3 km also indicates that the lower limit is about 2 cm for earthquakes of magnitude about 7 when SMBLOC method is used. -
日本K-NET和KiK-net提供了强震动波形资料，日本国土地理院提供了GPS数据，两位审稿人提出了建设性意见，作者在此表示诚挚的感谢.
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图 1 2016年4月16日日本熊本MW7.0地震震中周围强震台站和GPS台站分布图
Figure 1. Distribution of strong motion and GPS stations around the 2016 Kumamoto MW7.0 earthquake
F1: Futagawa fault; F2: Hinagu fault; F3: Midorikawa fault. The red triangles are the K-NET strong motion stations, the purple triangles are the KiK-net strong motion stations, and the blue diamonds are the GSI continuous GPS stations. The purple line is the intersecting line of the given fault plane (the purple dashed rectangle) with the ground
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图 2 KMMH162台站(Δ=7.4 km)基线校正前(a)、后(b)加速度(左)、速度(中)和位移(右)时程图
Figure 2. Uncorrected (a) and corrected (b) acceleration (left), velocity (middle) and displacement (right) at the station KMMH162, 7.4 km from the epicenter
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图 3 熊本地震基于强震(红色)和GPS(蓝色)记录所得的水平(a)和垂直(b)位移场的对比
Figure 3. Comparison of coseismic horizontal (a) and vertical (b) displacement fields based on the strong motion (red) with those from GPS (blue) The purple line is the intersecting line of the given fault plane (the purple dashed rectangle) and the ground
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图 4 台间距在3 km以内的12对GPS(蓝色)和强震(红色)台站对同震位移解算结果的对比
Figure 4. Comparison of coseismic displacements on 12 station-pairs of GPS (blue) and strong motion (red) with interval less than 3 km
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图 5 近场强震(a)、GPS(b)和二者联合(c)位移场反演的震源滑动模型
Figure 5. Slip models inverted from the coseismic displacements by near-field strong-motion (a), GPS (b) and their combination (c)
表 1 反演所用的熊本地区Crust1.0地壳速度模型
Table 1 Crustal velocity model Crust1.0 for slip model inversion in Kumamoto
地壳分层/km vP/(km·s-1) vS/(km·s-1) 密度/(g·cm-3) 0—1 2.50 1.20 2.10 1—11 6.00 3.40 2.70 11—21 6.60 3.70 2.90 21—31 7.20 4.00 3.10 ≥31 8.08 4.47 3.38 
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表 2 基于相同断层面参数使用不同资料反演所得滑动模型结果比较
Table 2 Comparison of slip models inverted by GPS, strong motion and their combination based on the same fault parameters
MW 数-模相关系数 平均滑动/m 最大滑动/m 平均应力降/MPa 最大应力降/MPa GPS 7.09 0.99 0.70 5.87 5.84 22.18 强震 7.12 0.99 0.78 5.10 3.53 18.89 GPS-强震 7.11 0.99 0.75 5.56 4.83 21.19
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