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Depths of Earthquakes in South Africa

机译：南非地震深处

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Historically, hypocentral depths of earthquakes in South Africa are not well documented from instrumentally determined parameters. We, therefore, investigated a concise number of earthquakes in South Africa over a broad geographical region. We reviewed the hypocentral depths of instrumentally recorded tectonic earthquakes in South Africa through synthetic waveform modeling and through a separate study using multiple phase arrivals. The resulting depths of earthquakes in South Africa occur at shallow crustal depths. It is further shown that uncertainty in focal depth is higher using the multiphase method in comparison with the regional depth-phase modeling method. Methodology tor determining focal depth from macroseismic observations is introduced in this article; however, poor coverage of intensity observations within the epicentral area limited the reliability of this method. Therefore, the study of hypocentral depths inferred from macroseismic observations was inconclusive, resulting from limited intensity data. Shallow depths are, however, inferred from the spatial patterns that do not exhibit the characteristic intensity patterns of deep earthquakes. It was noted during this study that the majority of events display the distinguishable isoseismal pattern of shallow earthquakes, whereas only a selected number of earthquakes exhibit spatial patterns expected of deeper crustal events. The present study did not find conclusive evidence of earthquakes occurring in the lower crust of South Africa from the limited number of earthquakes considered, which therefore indicates a unimodal depth distribution of earthquakes in the upper crust between the depths of 3 and 20 km. This observation contradicts reports in internationally published earthquake catalogs that indicate deeper earthquakes for individual events, for example, the Mw ~ 6.2 1969 Ceres earthquake.
机译：从历史上看，南非地震的斜视深度从乐器确定的参数没有充分记录。因此，我们在广泛的地理区域上调查了南非的南非地震。我们通过合成波形建模和使用多阶段抵达的单独研究审查了南非乐器录制的构造地震的斜视深度。南非地震所产生的深度发生在浅层地壳深度。进一步表明，与区域深度相位建模方法相比，使用多相方法的局灶性深度的不确定性更高。在本文中介绍了从宏观造成观察结果中确定局部深度的方法。然而，震中区域内的强度观测的覆盖率差限制了这种方法的可靠性。因此，从大乳糖性观察中推断的斜视深度的研究是不确定的，由有限的强度数据产生。然而，从不表现出深层地震的特征强度模式的空间模式推断出浅深度。在这项研究期间注意到，大多数事件显示了浅地震的可区分的奇异模式，而只有选定数量的地震表现出预期的地壳事件的空间模式。目前的研究没有找到从被认为有限的地下地区的南非地壳发生的地震发生的决定性证据，因此表明，在3到20公里的深度之间的地壳中，地壳中的地震的单级深度分布。该观察结果与国际公布的地震目录中的报告相矛盾，这些地震目录表明各个事件的深层地震，例如，MW〜6.2 1969年的地震。

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