TAILIEUCHUNG - Physical Processes in Earth and Environmental Sciences Phần 7

Chương 4 Động đất và căng thẳng Trong phần giới thiệu chương này, chúng tôi ghi nhận động đất đã được đánh dấu bởi phát hành của năng lượng địa chấn cùng máy bay gãy cắt. | 190 Chapter 4 Earthquakes and strain In the introduction to this chapter we noted that earthquakes were marked by release of seismic energy along shear fracture planes. This energy is released partly as heat and partly as the elastic energy associated with rock compression and extension. In the elastic rebound theory of faults and earthquakes the strain associated with tectonic plate motion gradually accumulates in specific zones. The strain is measurable using various surveying techniques from classic theodolite field surveys to satellite-based geodesy. In fact the earliest discovery of what we may call preseismic strain was made during investigations into the causes of the San Francisco earthquake of 1906 when comparisons were made of surveys documenting m of preearthquake deformation across the San Andreas strike-slip fault. We have already featured the results of modern satellite-based GPS studies in deciphering ongoing regional plate deformation in the Aegean area of the Mediterranean Section . All such geodetical studies depend upon the elastic model of steady accumulating seismic strain and displacement. But then suddenly the rupture point Section is exceeded and the strained rock fractures in proportionate or equivalent magnitude to the preseismic strain. This coseismic deformation represents the major part of the energy flux and is dissipated in one or more rupture events order 10 2-101 m slip . The remainder dissipates over weeks or months by aftershocks as smaller and smaller roughness elements on the fault plane shear past each other until all the strain energy is released. If the fault responsible breaks the Earth s surface then the coseismic deformation is that measured along the exposed fault scarp whose length may reach tens to several hundreds of kilometers. Different types of faults give rise to characteristic first motions of P-waves and it is this feature that nowadays enables the type of faulting responsible for an .

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