Search results
Results From The WOW.Com Content Network
In seismology, the depth of focus or focal depth is the depth at which an earthquake occurs. Earthquakes occurring at a depth of less than 70 km (43 mi) are classified as shallow-focus earthquakes, while those with a focal depth between 70 km (43 mi) and 300 km (190 mi) are commonly termed mid-focus or intermediate-depth earthquakes. [1]
The path of deep-focus earthquake seismic waves from focus to recording station goes through the heterogeneous upper mantle and highly variable crust only once. [3] Therefore, the body waves undergo less attenuation and reverberation than seismic waves from shallow earthquakes, resulting in sharp body wave peaks.
Deep-focus earthquakes occur at a depth where the subducted lithosphere should no longer be brittle, due to the high temperature and pressure. A possible mechanism for the generation of deep-focus earthquakes is faulting caused by olivine undergoing a phase transition into a spinel structure. [22]
Deep-focus earthquake, also called a plutonic earthquake, an earthquake with a depth exceeding 70 kilometres (43 mi). [5] Doublet earthquake, an earthquake that consists of at least two or more mainshocks of nearly identical magnitude, separated by a period of time. [6]
Moderately damaging earthquakes strike between New York and Wilmington, Delaware, about twice a century, the USGS said, and smaller earthquakes are felt in the region roughly every two to three years.
Surface waves are smaller for deep earthquakes, which have less interaction with the surface. For shallow earthquakes – less than roughly 60 km deep – the surface waves are stronger, and may last several minutes; these carry most of the energy of the quake, and cause the most severe damage.
Hypocenter (Focus) and epicenter of an earthquake. An earthquake's hypocenter or focus is the position where the strain energy stored in the rock is first released, marking the point where the fault begins to rupture. [3] This occurs directly beneath the epicenter, at a distance known as the hypocentral depth or focal depth. [3]
The Mohorovičić discontinuity was first identified in 1909 by Mohorovičić, when he observed that seismograms from shallow-focus earthquakes had two sets of P waves and S waves, one set that followed a direct path near the Earth's surface and the other refracted by a high-velocity medium. [4]