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Earthquake location in tectonic structures of the Alpine Chain: the case of the Constance Lake (Central Europe) seismic sequence

D’Ajello Caracciolo Francesca, Console Rodolfo

Acta Geophysica

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2021

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Vol. 69, no. 4

1163--1175

EN

A set of four magnitude Ml≥3.0 earthquakes including the magnitude Ml=3.7 mainshock of the seismic sequence hitting the Lake Constance, Southern Germany, area in July–August 2019 was studied by means of bulletin and waveform data collected from 86 seismic stations of the Central Europe-Alpine region. The frst single-event locations obtained using a uniform 1-D velocity model, and both fxed and free depths, showed residuals of the order of up±2.0 s, systematically afecting stations located in diferent areas of the study region. Namely, German stations to the northeast of the epicenters and French stations to the west exhibit negative residuals, while Italian stations located to the southeast are characterized by similarly large positive residuals. As a consequence, the epicentral coordinates were afected by a signifcant bias of the order of 4–5 km to the NNE. The locations were repeated applying a method that uses diferent velocity models for three groups of stations situated in diferent geological environments, obtaining more accurate locations. Moreover, the application of two methods of relative locations and joint hypocentral determination, without improving the absolute location of the master event, has shown that the sources of the four considered events are separated by distances of the order of one km both in horizontal coordinates and in depths. A particular attention has been paid to the geographical positions of the seismic stations used in the locations and their relationship with the known crustal features, such as the Moho depth and velocity anomalies in the studied region. Signifcant correlations between the observed travel time residuals and the crustal structure were obtained.

2

Extending the double-difference location technique to mining applications part I: Numerical study

Rudziński Ł., Dębski W.

Acta Geophysica

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2011

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Vol. 59, no. 4

785-814

EN

The location of the seismic event hypocenter is the very first task undertaken when studying any seismological problem. The accuracy of the solution can significantly influence consecutive stages of analysis, so there is a continuous demand for new, more efficient and accurate location algorithms. It is important to recognize that there is no single universal location algorithm which will perform equally well in any situation. The type of seismicity, the geometry of the recording seismic network, the size of the controlled area, tectonic complexity, are the most important factors influencing the performance of location algorithms. In this paper we propose a new location algorithm called the extended double difference (EDD) which combines the insensitivity of the doubledifference (DD) algorithm to the velocity structure with the special demands imposed by mining: continuous change of network geometry and a very local recording capability of the network for dominating small induced events. The proposed method provides significantly better estimation of hypocenter depths and origin times compared to the classical and double-difference approaches, the price being greater sensitivity to the velocity structure than the DD approach. The efficiency of both algorithms for the epicentral coordinates is similar.

3

Non-linear optimization methods for small earthquake locations

Pszczoła G., Leśniak A.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2004

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Vol. 8, No 4

583-590

EN

The problem of locating mine tremors using P-wave arrival times is revisited in the paper. A multidimensional, global, non-linear, constrained optimization method is used as a minimization algorithm for tremor location.In order to see the general properties of the minimized function a few images showing its basins of attractions have been constructed. These pictures enable us to choose efficient algorithms needed to solve location problems. The classical genetic algorithm, pure random search and the most efficient multistart algorithm have been tested. Local minimization methods should be introduced to the location procedure to increase the efficiency of tremor location.