The earth moved: but how fast? | University of Oxford
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The earth moved: but how fast?

Pete Wilton

We all woke up this morning to be reminded that the earth doesn't always sit placidly under our feet. Yet the earthquake the UK experienced in the early hours of this morning doesn't bear comparison with the catastrophic quakes of the past or ones predicted for the future. According to Shamita Das from Oxford's Department of Earth Sciences the severity of particular quakes may be down to speedy 'super-shear' waves travelling down the straight portions of faults at twice the speed of the original shockwave. In her comparison of data from the the 1906 California earthquake with data from a similar earthquake that occurred in 2001 in Kunlunshan, Tibet, she found that these 'super-shear' waves could explain why similar magnitudes of earthquake can cause much greater devastation in some areas than others. 'Long straight faults are more likely to reach high rupture speeds,' Shamita commented. 'The fault starts from rest, then accelerates to the maximum permissible speed and continues at this speed until it reaches an obstacle such as a large 'bend'. If the next earthquake in southern California follows the same pattern as the ones in California in 1857 and 1906, and in Tibet in 2001, a super-shear rupture travelling southward would strongly focus shock waves on Santa Barbara and Los Angeles.' Shamita is currently in San Francisco continuing her research, so she missed the UK's latest teacup rattling moment. Let's all be grateful that Britain lacks California's long, straight 'freeway' faults.