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Identification of the Mechanisms of the Seasonal Crustal Deformation

季节性地壳变形机制的识别

基本信息

批准号：
13640430
负责人：
HEKI Kosuke
金额：
$ 1.02万
依托单位：
National Astronomical Observatory
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2002
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-13640430/
关键词：
GPS Crustal Deformation Seasonal Variation Continuous Observation Snow Load Earthquake Triggering Space Geodesy VERA

项目摘要

Distinct periodic variations with annual frequencies are often found in the time series of continuous Global Positioning System (GPS) site coordinates in northeastern Japan. They show maximum arc-normal contraction of a few millimeters as well as maximum subsidence of 1-2 centimeters, both in March. In northeastern Japan, it snows heavily on the western flank of the backbone range, attaining the maximum depth of up to a few meters in March. We showed that the surface loads caused by the snow are largely responsible for the annual displacement of GPS sites, by comparing the load distribution estimated from the GPS data and the observed snow depths.Snow load along the western flank of the backbone range of the Japanese Islands perturbs the interseismic strain buildup, and may seasonally influence the seismicity in Japan. Intraplate earthquakes in northeastern Japan occur on reverse faults striking parallel with the snow-covered zone. In central and southwestern Japan, they occur on strike-slip faults striking either parallel with, or perpendicular to the snow cover. The snow load enhances compression at these faults, reducing the Coulomb failure stress by a few kPa. This is large enough to modulate the secular stress buildup of a few tens of kPa/yr. Past destructive inland earthquakes with magnitudes >7.0 that occurred in regions covered with snow in winter, tend to occur more in spring and summer than in autumn and winter, while those in the snow-free regions do not show such variation. Although its statistical significance is not strong due to limited number of past earthquakes, it suggests that the spring thaw enhances seismicity beneath the snow cover. Well-known annual variation of offshore interplate seismicity cannot be explained by the snow load, and might be driven by other mechanisms such as change in ocean loads. This needs substantiation by ocean bottom pressure gauge observations.

日本东北部地区连续GPS站点坐标的时间序列显示出明显的年频率周期性变化。它们显示出最大的弧形正常收缩几毫米，最大的下沉1-2厘米，都在3月份。在日本东北部，主干山脉的西侧积雪很大，三月份的积雪深度最大可达几米。结果表明，积雪引起的地表荷载是造成GPS站点年位移的主要原因。日本列岛主干带西侧翼的雪荷载扰动了地震间应变的积累，并可能对日本的地震活动性产生季节性影响。日本东北部的板内地震发生在与积雪覆盖区平行的反向断层上。在日本中部和西南部，它们发生在与积雪平行或垂直的走滑断层上。雪荷载增强了这些断层处的压缩，使库仑破坏应力降低了几个kPa。这足以调节几十千帕/年的长期应力积累。以往发生在冬季积雪地区的bb0 ~ 7.0级破坏性内陆地震，春、夏两季多发生于秋冬两季，而无积雪地区则没有这种变化。虽然由于过去地震次数有限，其统计意义不强，但这表明春季解冻增强了积雪下的地震活动性。众所周知，近海板块间地震活动性的年变化不能用雪荷载来解释，而可能由其他机制驱动，如海洋荷载的变化。这需要海底压力计的观测来证实。