1997-1998年巴西Senador Sa-CE Tucunduba水库的地震活动性
Seismic Activity in Tucunduba Reservoir, Senador Sa-CE, Brazil, 1997-1998
摘要：
Tucunduba大坝位于塞阿拉州福塔莱萨以西约290公里处。1997年6月9日发生$m_b$ 3.2级地震后不久，1997年6月11日开始对该地区进行地震监测。监测是由一个模拟站（用于震级持续时间测量和统计控制活动）和七个数字站完成的。这些数字电台各有三个组成部分，于1997年6月至11月运行。在这项工作中，在数字化监测过程中收集的数据进行分析，以确定震源和震源机制。用HYPO 71程序确定震源，采用半空间模型，P波速度参数为5.95km/s，P/S波速度比为1.69。活动带长近1公里，深度在4.5至5.2公里之间。利用6个台站共记录到的16个地震，确定了断裂面的走向（NE-SW）。断裂机制为走滑，具有较小的正向分量。使用FPFIT时，下降估计值为65 $^{\circ}$ SE，使用FOCMEC时，下降估计值为80 $^{\circ}$ SE。使用P轴方向对最大水平压应力的初步估计与Ferreira { \it et al.}（1998年）。这种微小的差异可能是由于区域应力中沉积盆地的影响。活动区与Assumpção（1998）描述的地震活动性一致，即：例如，区域应力、厚沉积负荷的局部挠曲效应以及中生代减薄的可能较弱地壳的组合。
英文摘要：
The Tucunduba Dam is about 290 km West of Fortaleza, Ceará state. The seismic monitoring of the area, with a local network, has began on June 11, 1997, soon after the occurrence of the event with magnitude 3.2 $m_b$ on June 09, 1997. The monitoring was done with one the analogical station (used for magnitude duration measurement and statistical control activity) and seven digital stations. The digital stations, with three components each, were operated from June to November 1997. In this work, the data collected during digital monitoring was analyzed to determine hypocenters and focal mechanism. To determine hypocenters, the HYPO71 program was used, with half-space model, whose parameters were 5.95 km/s, for P-wave velocities, and 1.69 for the ratio between P and S-wave velocity. The active zone was nearly 1 km length, with depth between 4.5 and 5.2 km. With 16 events recorded in the same six stations, we determined the direction of the fault plane (NE-SW). The fault mechanism is strike-slip with a small normal component. The dip estimate was 65$^{\circ}$SE with FPFIT and 80$^{\circ}$SE with FOCMEC. Preliminary estimates of maximum horizontal compressive stress, using P-axis direction, were in accordance with Ferreira {\it et al.}(1998). The small difference is probably due to influence of the sedimentary basin in the regional stress. The active area is in accordance with seismicity described by Assumpção (1998), i. e., the combination regional stress, local flexural effect from thick sedimentary loads, and a presumably weaker crust from Mesozoic thinning.
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