We calculated apparent stresses for 70 earthquakes ( M W ≥ 5.0) occurring in the aftershock region of the 2010 M W 8.8 Bio-Bío earthquake from January 1990 to September 2019. We identified that the average apparent stress was approximately 0.487 MPa between January 1990 and December 2005 and approximately 1.063 MPa within the period from January 2006 to January 2010. The latter one is 2.2-fold greater than the former, representing a significant difference as determined by a z test, with a 99% confidence level. Moreover, we analyzed the temporal evolution of the apparent stress and found that apparent stress rapidly increased from 0.43 to 1.2 MPa during the pre-event period from March 2006 to the occurrence of the Bio-Bío M W 8.8 mainshock, and this increased apparent stress was found to be significant at the 98% confidence level. Furthermore, we calculated the spatial distribution of the apparent stress in the study region and observed two higher-apparent-stress regions, within one of which the epicenter of the M W 8.8 event was located. On the basis of the inverse correlation between b value and stress, the temporal evolution and spatial distribution of b values were calculated and compared with those of the apparent stress. The comparison showed that the b values decreased approximately 4 years before the occurrence of the mainshock, while the apparent stress increased substantially; for the region of lower b , the apparent stress is higher, and vice versa. Therefore, the inverse correlation between b value and stress is supported by the results obtained in the present study and can be probably considered as one of the precursors to great earthquakes.

中文翻译：

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2010 年智利 Mw8.8 Bio-Bío 地震前表观应力和 b 值的变化

我们计算了 1990 年 1 月至 2019 年 9 月发生在 2010 年 MW 8.8 Bio-Bío 地震余震区的 70 次地震（MW ≥ 5.0）的表观应力。我们确定 1990 年 1 月至 2005 年 12 月的平均表观应力约为 0.487 MPa 2006 年 1 月至 2010 年 1 月期间约为 1.063 MPa。后者比前者大 2.2 倍，通过 az 检验表明差异显着，具有 99% 的置信水平。此外，我们分析了表观应力的时间演变，发现从 2006 年 3 月到 Bio-Bío MW 8.8 主震发生的前期，表观应力从 0.43 MPa 迅速增加到 1.2 MPa，这种增加的表观应力是发现在 98% 的置信水平上显着。此外，我们计算了研究区域表观应力的空间分布，并观察到两个较高的表观应力区域，其中一个 MW 8.8 事件的震中位于其中。根据b值与应力的反相关关系，计算b值的时间演化和空间分布，并与表观应力进行比较。对比表明，主震发生前大约4年，b值下降，而视应力显着增加；对于 b 较低的区域，表观应力较高，反之亦然。因此，本研究的结果支持了 b 值与应力之间的负相关性，可以认为是大地震的前兆之一。