UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS

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2024-11-22 2:37
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Conference: Bucharest University Faculty of Physics 2010 Meeting


Section: Atmosphere and Earth Science; Environment Protection


Title:
Calibrating the local magnitude formula ML using modified Richter formula, reported with the MD magnitude


Authors:
M.Craiu, Andreea Craiu, C.Ionescu


Affiliation:
NIEP, Magurele-Bucharest, Romania.


E-mail
gcraiu@infp.ro


Keywords:
magnitude, earthquakes, seismogram


Abstract:
The seismic activity on the Romanian territory consists of both shallow and intermediate-depth earthquakes. The subcrustal activity is concentrated at the bend of the Carpathian arc (Vrancea region) within a confined focal volume in the depth range from 60 to 180 km.The subcrustal earthquakes generated here are of the largest magnitude throughout the Carpathians (Mw=7.7 maximum recorded magnitude). The crustal seismicity is moderate and more scattered in comparison with the intermediate-depth one. The purpose of this paper is to revise the local magnitude formula for the depth-intermediate Vrancea earthquakes. In order to calibrate and compare the magnitude scales used in the present work, we have to use a reference scale. For our study we have chosen the local magnitude scale definited by Richter (1958). The revised scale by Hutton and Boore (1987) is given as: ML = log10(A) + 1.11 log10R + 0.0019*R – 2.09, Where A is the maximum amplitude measured in mmwa using a filter simulating the low-frequency cutoff of a Wood-Anderson seismometer; R is the hipocentral distance measured in km. Using as reference the MD magnitude, and using the modified Richter relation, assumed by the IASPEI working group, we have determined new coefficients (c0-c4) through the multiple regression method. The amplitude (A) was measured on the horizontal components of a broad band sensor in millimeters on the synthetic Wood-Anderson seismogram.We used a data base formed by a set of 467 depth-intermediate earthquakes with magnitudes MD= 2.3-5.7 and depths of 70-150 km, occurred between 2007-2009. Comparing the results obtained by this new relation with the MD values, we discovered an average error of ± 0.18 units (ML=MD ± 0.18).