Geodetic Observation of Surface Displacements from the Great Bolivian Deep Earthquake

9521921 Stein这项研究将利用一个非同寻常的机会，利用基于空间的大地测量来研究地球深处的过程。1994年6月9日，地震学记录的最大深部地震发生在玻利维亚北部地下650公里处。距离震中9000公里的西雅图和多伦多都能感觉到地面运动，这一事实说明了它的非凡规模。这场地震已经成为密集的地震学研究的焦点，因为在这些极端深度允许地震破坏的物理过程是一个长期悬而未决的问题。虽然大地测量研究以前从未被用来研究深部地震，但在这种情况下，它们是实用的。根据地震学观测和理论计算，这次地震如此之大，以至于震中上方可能出现厘米级的静态位移。幸运的是，首席调查人员在玻利维亚建立了一个大地测量网络，并在地震前一个月使用全球定位系统进行了测量。因此，对该网络的重新调查将产生对深震后静态位移的第一次直接观测。大地测量和地震学结果的比较将特别有价值，因为引起深部地震的物理过程仍然未知，但很可能与浅层地震的物理过程非常不同。特别是，由于深部地震机制的主要但有争议的模型是它们是由固态相变引起的，所以同震形变和长期形变之间可能存在显著差异。时间至关重要，因为大地测量网络的建立是为了测量与跨越安第斯山脉的缩短相关的预期稳态变形。因此，时间过得越久，将地震的影响与构造缩短区分开来的可能性就越小。此外，通过与一个计划于1995年5月在玻利维亚进行测量的德国小组合作，可以显著降低测量地震影响的成本。尽管德国在地震前计划的研究本身不足以解决地震位移问题，但在额外测量方面的适度投资将有助于共同实现这一目标。这项研究是由探索性研究小额拨款计划资助的，是国家减少地震风险计划的一部分。***

9521921 Stein This research will take advantage of an extraordinary opportunity to use space-based geodesy to study a deep earth process. On 9 June 1994, the largest deep earthquake ever seismologically recorded occurred 650 km beneath Northern Bolivia. Its extraordinary size is illustrated by the fact that ground motion was felt as far away as Seattle and Toronto, 9000 km from the epicenter. This earthquake has become the focus of intensive seismological study, because the physical process permitting seismic failure at these extreme depths is a long-standing unresolved question. Although geodetic studies have never been previously used to study a deep earthquake, they are practical in this case. The earthquake is so large that centimeter-level static displacements above the hypocenter appear likely, based on both seismological observations and theoretical calculations. Through good luck, the Principal Investigators established a geodetic network in Bolivia and measured it using the Global Positioning System only a month before the earthquake. Hence a resurvey of the network would yield the first direct observation of static displacements following a deep earthquake. The comparison of geodetic and seismological results would be especially valuable because the physical process causing deep earthquakes is still unknown, but is most likely very different from that for shallow earthquakes. In particular, because the leading but controversial model for the mechanism of deep earthquakes is that they result from solid state phase changes, there may be significant differences between coseismic and long term deformation. Time is of the essence, because the geodetic network was established to measure the expected steady-state deformations associated with shortening across the Andes. As a result, the more time that passes, the poorer the chances of separating the effects of the earthquake from the tectonic shortening. Moreover, the cost to measure the earthquake effects can be reduced significantly by cooperation with a German group who plan measurements in Bolivia in May, 1995. Although the German study, which was planned before the earthquake, would by itself be inadequate to resolve the earthquake displacement, a modest investment in additional measurements would permit joint achievement of the goal. This research is funded under the Small Grants for Exploratory Research program and is a component of the National Earthquake Hazard Reduction Program. ***