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Magnitude relations between the teleseismic mb, the regional mR and Mw for intraplate earthquakes in Brazil
Journal of South American Earth Sciences ( IF 1.8 ) Pub Date : 2022-09-27 , DOI: 10.1016/j.jsames.2022.104038
Marcelo Assumpção, Juraci M. Carvalho, Fábio L. Dias, Stéphane Drouet, José Roberto Barbosa, Marcelo Belentani de Bianchi, Bruno Collaço

Magnitude conversions between different scales are important for comparison of seismic activity between different regions, homogenization of earthquake catalogs for seismic hazard calculations, and use of ground motion relations derived from other regions. Despite the trend of adopting Mw as the standard, reference magnitude scale, other scales are still much used for practical reasons and ease of calculation, such as the local ML for events detected by local networks, and short-period teleseismic mb for events in worldwide catalogues. In Brazil, a regional magnitude (mR), based on the maximum amplitude in the whole P-wave train recorded between 200 and 1500 km distance, has been adopted in our catalogues. The regional magnitude is equivalent to the teleseismic mb from 3.5 to 5.5.

Empirical relations between the regional (mR), the teleseismic (mb) and the moment (Mw) magnitudes were determined for Brazilian intraplate earthquakes. Mw can be estimated from m by Mw = 1.10 m - 0.69. In this empirical relation, “m" is mb, mR, or the average of the two. However, despite the average consistency of the regional (mR) and teleseismic (mb) scales, it has been found that difference between mb and mR depend on the type of faulting mechanism: mb > mR for dip-slip earthquakes (reverse and normal faulting), and mb < mR for strike-slip events. This can be explained by the differences in the average radiation patterns of upper crustal earthquakes recorded at regional distances (more horizontally oriented take-off angles) or at teleseismic distances (more vertically oriented take-off angles). This brings the possibility to use the difference between regional and teleseismic magnitudes to indicate the probable type of focal mechanism.



中文翻译:

巴西板内地震远震mb、区域mR和Mw的震级关系

不同尺度之间的震级转换对于比较不同区域之间的地震活动、地震目录的同质化以进行地震危险性计算以及使用来自其他区域的地震动关系具有重要意义。尽管有采用 Mw 作为标准、参考震级尺度的趋势,但出于实际原因和易于计算的原因,其他尺度仍然大量使用,例如本地网络检测到的事件的本地ML ,以及全球事件的短周期远震mb目录。在巴西,区域震级 ( m R),基于在 200 至 1500 公里距离之间记录的整个 P 波列的最大幅度,已在我们的目录中采用。区域震级相当于远震mb从3.5到5.5。

区域 ( m R )、远震 ( mb ) 和力矩 ( Mw ) 震级之间的经验关系是针对巴西板内地震确定的。Mw可以通过Mw  = 1.10  m - 0.69从m估算。在这个经验关系中,“ m ”是mbm R,或者是两者的平均值。然而,尽管区域(m R)和远震(mb)尺度的平均一致性,已经发现mb和m R之间的差异R取决于断层机制的类型:对于倾滑地震(反向和正断层),mb  >  m R,对于走滑事件, mb  <  m R。这可以通过在区域距离(更水平方向的起飞角度)或远震距离(更垂直方向的起飞角度)记录的上地壳地震的平均辐射模式的差异来解释。这带来了使用区域和远震震级之间的差异来指示可能的震源机制类型的可能性。

更新日期:2022-09-27
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