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The point along a fault where an earthquake is initiated.



the focal point of an earthquake. The depth at which a hypocenter lies can vary from 0 to 700 km. The source of underground shock is movements along tectonic faults, which vary in length up to hundreds of kilometers. In this sense, the hypocenter means the point from which the fault began to rip open. In the upper parts of the earth’s crust (up to 20 km) the hypocenter occurs as a result of brittle deformations in a rock series. Deeper hypocenters arise where plastic deformations prevail.

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This was done as an effort to reduce the errors in the hypocentral locations determined by ISC and NEIC, since this method permits a better constrained estimate of the focal depth when a considerable number of pP phases are included.
Ten of the selected earthquakes have shallow hypocentral depths (h [less than or equal to] 70km), one earthquake has an intermediate hypocentral depth (70km [less than or equal to] h [less than or equal to] 140km), and four earthquakes have deep hypocentral depth (h>140km).
Earthquake Hypocentral and Fault Plane Solution Data obtained in this study.
Perpendicular hypocentral projections and along the arc were done following the propose methodology by Guzman, S (1995).
0] = epicentral intensity, R = hypocentral distance (km), D = epicentral distance (km); ML = local magnitude; h = depth of focus (km), M = magnitude; b, d, [alpha], are constants.
After calculating the hypocentral parameters for all earthquakes, those with RMS travel time residual <0.
In the worst case, changes of hypocentral were lower than 5 km, but in most cases those variations were smaller than 3 km.
At distances larger than 400 km east of the central Andes the hypocentral parameters are not well constrained, and are assumed to be distributed nearly horizontally at 120 km-depth, as observed in Figure lb (dashed line).
These earthquakes were later relocated using the Joint Hypocentral Determination (JHD), (Dewey, 1971) in order to verify the quality of the model generated for this zone (Espinosa y Monsalve 2002).
2] (from zero to maximum) registered by an accelerograph set on the bedrock for a particular earthquake at a specified distance and A is the hypocentral distance in km.