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991.
992.
Undead earthquakes 总被引:1,自引:0,他引:1
This short communication deals with the problem of fake earthquakes that keep returning into circulation. The particular events discussed are some very early earthquakes supposed to have occurred in the U.K., which all originate from a single enigmatic 18th century source. 相似文献
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Earthquake mechanisms in the Hellenic Trench near Crete 总被引:1,自引:0,他引:1
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Pseudotachylyte formation is typically viewed as a self-limiting process. Quantitative models have demonstrated that frictional melting is possible at seismic slip rates, but once a thin film of melt forms on a seismic fault plane, the dramatic decrease in fault friction is thought to suppress further melting. Volumes of melt-generated pseudotachylyte observed in field studies, however, are in many cases substantially larger than the amounts of frictional melt predicted by theoretical models. This suggests that previously unrecognized physical processes may enhance melting during seismic slip. Localized decompression at dilational jogs may be one such phenomenon. Transient unloading could play two important roles in the dynamics of pseudotachylyte generation. First, by setting up significant fluid pressure gradients, it would lead to rapid migration of the melt to sites of low pressure, thereby reestablishing frictional contact across the fault surface and favoring further melt generation. Second, at significant depths, sudden depressurization might lead to in situ decompression melting. 相似文献
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This paper presents a study of the damage due to the Mw 7.6–7.7 intraplate Kutch earthquake of 26 January 2001. It was a powerful earthquake with a high stress drop of about 20 MPa. Aftershocks (up to M 4) have continued for 2.5 years. The distribution of early aftershocks indicates a rupture plane of 20–25 km radius at depths of 10–45 km along an E–W-trending and south-dipping hidden fault situated approximately 25 km north of the Kutch Mainland Fault. The moment tensor solution determined from regional broadband data indicates reverse motion along a south-dipping (by 47°) fault. The earthquake is the largest event in India in the last 50 years and the most destructive in the recorded history in terms of socioeconomic losses with 13,819 deaths (including 14 in Pakistan), collapse/severe damage of over a million houses and US$10 billion economic loss. Surface faulting was not observed. However, intense land deformations have been observed in a 40×20-km meizoseismal area. These include lateral spreading, ground uplifts (about a meter), ground slumping and deep cracks. Liquefaction with ejection of sand and copious water was widespread in the Banni grassland, Rann areas (salt plains), along rivers and also in the coastal areas up to 200 km distance from the epicenter in areas of intensity VII to X+. Stray incidences of liquefaction have occurred up to distances of at least 300 km. For the first time in India, multistory buildings have been destroyed/damaged by an earthquake. The maximum acceleration is inferred to be 700 cm/s2 and intensities are 1–3 units higher in soil-covered areas than expected from the decay rate of acceleration for hard rock. 相似文献