Hypocenters calculation for volcanic earthquakes associated with movement of fluid in the Galeras volcano, Colombia

Abstract

One of the most important tasks in the volcanic seismology is the location of the seismic sources. Given the difficulty of identification of the seismic phases and the measurement of its arrival times, an algorithm develops for the determination of the hypocenter of these earthquakes based on the attenuation of the extents of the waveforms and the application of Gauss-Newton's method. The basic principle is the calculation of the hypocentral parameters of the earthquake by means of the simultaneous minimization of the residual ones of the extents of the waveforms from several observations. The method uses an adjustment of square minimums developed in a series of Taylor in its first approximation. It is considered to be a variation of the hypocentral parameters of an initial supposed location (initial model) and those have to by means of an iterative procedure minimize simultaneously the residues of the calculated extents and the observed ones of the records in a network of seismic stations. The investment of the extents to estimate the location of the seismic source is supported in a physical model of attenuation that describes the relation between the amplitudes and parameters of the source, taking into account the geometric amplitude, anelastic absorption, orientation of the seismometer components, effects of free surface and topography. The convergence of the solution strongly depends on the proximity of the initial model suppositions with reality.