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1999年台湾集集地震(MW7.6)加速度记录的高频带通滤波使连续信号分解为一系列持续时间相对短、能量离散的破裂。我们假设,这些破裂在单台附近以浅源小事件的形式起始,是由集集主震产生的P波和S波动态触发的;但是,我们也无法排除它们是由和地表相关的非地震因素,比如建筑物或树木,引起的可能性。破裂只在地震信号出现期间观测到,在信号噪声之前和之后均未观测到。因为多组由3台独立仪器共同定位的仪器组均记录到相同的破裂,因此这些破裂不可能是由仪器产生的。我们还指出,这些破裂也不是由仪器产生的阶梯函数的带通滤波引起的。它们是近震事件的假设得到在距震中达170km的距离观测到40Hz频段的破裂的支持。如果这些破裂如Chen等(2006)根据车笼埔断层20km以内记录的分析所假设的那样起始于集集断层面上,那么假定地壳衰减有任何合理的值,在这样的距离上它们都不应该被观测到。假设为近距离引起的,我们估计近震的平均震级是MW0.2,震源到接收器的距离约为1km。通过分析集集地震分析中使用的很多相同仪器记录的较小(MW5.3)事件的记录,将我们的分析扩大到更低的应力水平。对于本次事件,仅仅在相对靠近主震震源的台站记录的加速度图中观察到有破裂事件。对两次主震的数据集综合分析表明,触发的应力阈值是,S波触发为0.03～0.05MPa,P波触发为0.0013～0.0033MPa,与之前观测的面波触发范围一致。
The high-frequency band-pass filtering of the 1999 Taiwan Jiadian earthquake (MW7.6) acceleration record breaks down the continuous signal into a series of fractures with relatively short durations and energetic dispersions. We assume that these ruptures, starting as small shallow events near a single station, are triggered by the P-wave and S-wave dynamics produced by the main mains of the collection; however, we can not rule out that they are caused by surface-related non-earthquakes Factors, such as buildings or trees, cause the possibility. Bursts were observed only during the occurrence of a seismic signal and were not observed before and after the signal noise. Because multiple sets of instruments co-located by three separate instruments all record the same rupture, these ruptures can not be instrument-generated. We also point out that these ruptures are not caused by band-pass filtering of the step function of the instrument. They are support for the assumption that near-earthquakes have been ruptured at a frequency of 40 Hz at a distance of 170 km from the epicenter. If these ruptures originate on the surface of the collection fault plane, as Chen et al. (2006) estimated from an analysis recorded within a distance of 20 km from the Chegongpu fault, it is assumed that there is any reasonable value of the crustal attenuation at which distance none of them Should be observed. Assuming close proximity, we estimate the average magnitude of near-earthquakes as MW0.2 and the distance from the source to the receiver to be about 1 km. Our analysis was expanded to lower stress levels by analyzing the records of the smaller (MW5.3) events recorded by many of the same instruments used in the Cumulative Seismic Analysis. For this incident, a rupture event was observed only in the acceleration map recorded at a station relatively close to the mainshock source. A comprehensive analysis of the data sets of the two main shocks shows that the triggering stress threshold is that the S-wave trigger is 0.03-0.05MPa and the P-wave trigger is 0.0013-0.0033MPa, which is consistent with the previously observed surface wave triggering range.