© John Wiley & Sons Ltd
Edited By: Jean Braun, Georges Calas, Max Coleman, Carlo Doglioni, Klaus Mezger & Jason Phipps Morgan
Impact Factor: 2.758
ISI Journal Citation Reports © Ranking: 2015: 37/184 (Geosciences Multidisciplinary)
Online ISSN: 1365-3121
Using crowdsourced data to understand seismic wave propagation and seismic hazard
Modern technology allows members of the public to contribute to science in ways never before possible. Sbarra et al. have used crowdsourced data to investigate the areas where earthquakes are felt with a level of precision that would not have been possible a few years ago. They have found that intermediate-depth earthquakes in Greece can often be felt in Italy – much further from the epicentre than would normally be expected. But, these Greek earthquakes are only felt by people on the African side of the Africa-Eurasia plate boundary; people on the European side of the plate boundary do not feel the earthquake. This study has potential implications for seismic hazard, highlights the way in which seismic waves propagate through the lithosphere and helps us to understand the structure of this tectonically complicated area.
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Gondwana breakup: A questionable concept survived for decades
During past decades, there appeared to be agreement on the Jurassic separation of East and West Gondwana and the motion of Madagascar, together with Antarctica–India–Australia, along a single major, straight transform fault, termed the Davie Fracture Zone. Prevailing north–south directed extension was thought to have resulted in the formation of a major oceanic basin, the West Somali Basin, bounded by a 1000 km-scale transform margin in the west.
In the Focus Article ‘Gondwana breakup: no evidence for a Davie Fracture Zone offshore northern Mozambique, Tanzania and Kenya’, Klimke and Franke investigate this basic concept by interpreting new geophysical data and available vintage reflection seismic data, initially used to develop the transform margin model. They show that the generation of various features, previously interpreted as evidence for the Davie Fracture Zone, postdate all published age estimations for the oceanic crust in the West Somali Basin. Rather, these features originate from the modern East African Rift System and a Late Cretaceous inversion phase in East Africa. These results challenge the commonly supported transform margin concept and imply that certain parts of Gondwana reconstructions need to be reconsidered. The breakup of East and West Gondwana certainly was not simple and it is not only the position of Madagascar that needs to be re-evaluated. How exactly did the West Somali Basin open? Could there have been initial east–west extension, or a highly oblique propagating rift separating India and Madagascar from East Africa? Did the oceanic basin open via repeated ridge jumps?
There is certainly much that is still unknown about the structure of the continental margins around the West Somali Basin and the transition to oceanic crust, but, more generally, conjugate geological and geophysical markers across the continents need further exploration and integration to better understand this last disintegration of a Supercontinent. The Gondwana puzzle continues to be appealing and challenging.
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