Consequently, the primary caution regarding this second approach is that there must be a reproducible and transparent definition of both the geographic boundaries of each seismogenic zone and its expected kinematics.įor this aim, geodetic measurements provide an unmatchable, still underrated source of information to be used for an alternative selection method in the b-value estimation. For example, a rough definition of a seafloor spreading seismotectonic zone overpopulates the extensional-earthquake group with the transform-fault earthquakes, resulting in a mixed faulting mechanism style, which is expected to influence the b-value. In this case, the accuracy of the b-values determination is mainly related to the correctness of the seismotectonic model. In the second case, earthquakes are grouped using kinematic information from a regional seismotectonic model 10, 12. These processes are expected to influence the b-value 5. Though convergent settings characterize both, these geodynamic processes maintain substantial differences in fluid circulation, thermal state, and volcanic activity. Similarly, the thrust-faulting earthquake class mixes subduction-related and continental-convergent earthquakes. Notably, back-arc extension occurs near convergent boundaries behind the volcanic arc. The extension in back-arc regions leads to the stretching and thinning of the continental or oceanic crust, forming basins filled with sediment and volcanic deposits. In the former, a new basaltic crust creates with the asthenosphere upwelling at the oceanic ridges in divergent plate boundaries. In the first case, a simplistic choice driven by focal mechanisms defining a normal-faulting earthquake class may mix two contrasting geodynamic settings: for example, seafloor spreading and back-arc extension. Both selection methods can potentially cause a mixture of geodynamics settings or faulting/tectonic styles. Regarding global catalogs, several studies have reported a b-value around 1.0 for regions undergoing strike-slip regime, b-value > 1 in extensional settings, and b-value < 1 in compressional ones 9, 10, 11.įor assessing the relationship of the earthquake size distribution with the kinematics, two different strategies are generally used to quantify the b-value variations: a) analyzing the events according to the focal mechanisms b) proceeding to a definition of a seismotectonic zonation and then analyzing the earthquakes of each zone. Studies on regional catalogs correlate the b-value with the earthquakes’ depth: the shallower the event, larger the b-value 7, apart from peculiar anomalies of high b-values in some subduction zones 8. Therefore, it is of primary importance to understand its variability across different portions of the Earth’s crust and its correlations with other geophysical quantities. The b-value is a fundamental parameter for seismic hazard studies, particularly for probabilistic seismic hazard analyses, since it rules the percentage between small and large events 6. Earthquake kinematics and differential stress influence the b-value 3, 4, 5. This relation corresponds to an exponential distribution with a single parameter, the b-value 2. Where \(N\) is the number of events with magnitude \(\ge M\), and \(a\) and \(b\) are the parameters controlling the distribution.
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