A model for possible crustal deformation prior to a coming large interplate earthquake in the Tokai district, central Japan
A model for possible crustal deformation prior to a coming large interplate earthquake in the Tokai district, central Japan
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日本中部东海地区即将发生的大板间地震之前可能发生的地壳变形模型
DOI：
10.1785/bssa0890061401
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发表时间：
1999
影响因子：
3
通讯作者：
Tomowo Hirasawa
中科院分区：
文献类型：
--
作者：
N. Kato;Tomowo Hirasawa
我们通过应用实验室得出的摩擦定律来对地震周期进行数值模拟，以评估假想的东海地震之前可能发生的地壳变形，该地震预计将于不久的将来沿着日本中部的Suruga海槽发生。在俯冲带的二维模型中，假定摩擦力服从与速率和状态有关的摩擦定律，作用于板块界面。我们测试了摩擦定律的两个版本：所谓的慢度版本和滑移版本。我们根据东海地区过去大地震的历史文献和GPS观测估计的东海地区下板块界面现在的耦合状态来选择模型参数。对慢度和滑移型的模拟结果如下：(1)在地震间隔期，板块界面的耦合区域随时间变窄。(2)在地震间隔期的大部分时间内，内陆地壳以几乎恒定的速度收缩。在板间大地震发生前，收缩速率减小或由收缩向伸展转变。(3)地震前存在明显的地壳形变异常，地震前一天左右的最大振幅超过了东海地区安装的钻孔应变仪晴天时的噪声水平。(4)板块界面无震滑动的时空变化扰乱了未来地震震源体积周围的区域应力场，可能导致俯冲板块的前兆地震平静和俯冲板块小震震源机制的改变。在摩擦定律的慢度版本和滑移版本的结果中，最显著的区别是，在地震前，慢速版本的前移和地壳形变的幅度比滑移版本的大几倍。虽然目前的模型存在一定的模糊性，主要原因是摩擦定律的不完备性和观测数据对模型参数的约束不足，但通过预测的地壳形变与观测结果的比较，可以改进物理模型。因此，对东海地区的地壳形变和地震活动进行连续和集中的观测，对于定量了解该地区板间大地震前的滑动过程是很重要的。
We perform numerical simulations of a seismic cycle by applying a laboratory-derived friction law to evaluate possible crustal deformations prior to the hypothesized Tokai earthquake, which is expected to occur in the near future along the Suruga trough, central Japan. The frictional force obeying a rate- and state-dependent friction law is assumed to act on the plate interface in a 2D model of the subduction zone. We test two versions of the friction law: the so-called slowness version and the slip version. We select model parameters on the basis of historical documents about past large earthquakes in the Tokai district and the present coupling state of the plate interface beneath the Tokai district estimated by GPS observations. Simulation results for both the slowness and the slip version are as follows: (1) The coupling region of the plate interface becomes narrower with time in the interseismic period. (2) The inland crust contracts at a nearly constant rate for most of the interseismic period. The contraction rate decreases or a change from contraction to extension takes place before the occurrence of a large interplate earthquake. (3) Significant abnormal crustal deformation precedes the earthquake, and maximum amplitudes about one day before the earthquake exceed the noise levels in the case of clear weather of borehole strainmeters installed in the Tokai district. (4) The spatiotemporal variation of aseismic sliding on the plate interface perturbs the regional stress field around the source volume of the coming earthquake, leading possibly to precursory seismic quiescence in the overriding plate and a change in focal mechanisms of small earthquakes in the subducting slab. The most significant difference in the results between the slowness version and the slip version of the friction law is that amplitudes of preslip and crustal deformation just before earthquakes are several times larger for the slowness version than for the slip version. Although some ambiguity remains in the present model mainly because of the incompleteness of the friction law and the deficiency of observational data constraining model parameters, the physical model can be improved through the comparison of predicted crustal deformation with observations. Continuous and concentrated observations of crustal deformation and seismic activity are thus important in the Tokai district to understand quantitatively the sliding process preceding a large interplate earthquake there.