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Local and duration magnitudes in northwestern Italy, and seismic moment versus magnitude relationships

D. Bindi, D. Spallarossa, C. Eva and M. Cattaneo
Local and duration magnitudes in northwestern Italy, and seismic moment versus magnitude relationships
Bulletin of the Seismological Society of America (April 2005) 95 (2): 592-604

Abstract

In the present work, we develop some local magnitude scales for northwestern Italy based on vertical short-period records. This study is motivated by the possibility of applying the computed scales to an instrumental catalog of more than 25,000 local earthquakes, as this region has been continuously monitored by 12 short-period vertical-component (1C) stations since the mid-1980s. Furthermore, a digital network of three-component (3C) broadband or 5 second sensors has monitored northwestern Italy since 1996. Today, a significant number of earthquakes have been simultaneously recorded by both networks, allowing the calibration of the 1C local scale by using magnitudes computed according to a scale derived for the 3C digital network. Moreover, because station Sant' Anna di Valdieri houses both a 3C (code STV2) and 1C (code STV) sensors, the magnitude scales for the two networks can be developed using the same reference station. The magnitude scale M (sub L) = log A + log(R/100) + 0.0054(R - 100) + 3 - S is derived for the 3C digital network with the requirement that the correction S of station STV2 is zero. This scale is based on 10,057 maximum amplitudes (2822 earthquakes) computed from horizontal synthesized Wood-Anderson seismograms, in the hypocentral distance 10 to 310 km and in the range 0 < or = M (sub L) < or = 5. With respect to an earlier magnitude scale derived for the 3C network constraining the sum of all the station corrections to zero, the magnitudes predicted by the previous equations show an average bias of (-0.2 + or - 0.1), which can be ascribed to the different constraint applied to the station corrections. The magnitudes predicted by the scale for the 3C network are used to calibrate magnitude scales based on either total duration or maximum amplitude from synthesized Wood-Anderson seismograms computed for each short-period vertical recording. The magnitude scale obtained considering maximum amplitudes from vertical short-period recordings is M (sub L) = log A + log(R/100) + 0.0041 (R - 100) + 3 - S'. The reliability of the obtained magnitude scales is assessed using 827 earthquakes different from those we considered in the regression analysis. Finally, the following seismic moment versus local magnitude relations are valid in the Western Alps in the range 0 < M (sub L) < 4.5: log M (sub 0) = (0.92 + or - 0.01) M (sub L) (super 3C) + (17.38 + or - 0.08) log M (sub 0) = (0.95 + or - 0.01) M (sub L) (super 1C) + (17.36 + or - 0.01) where M (sub L) (super 3C) is the local magnitude computed starting from the horizontal component of broadband (flat frequency response, from 0.033 to 50 Hz) or semibroadband (flat frequency response, from 0.2 to 40 Hz) sensors and M (sub L) (super 1C) is the magnitude computed starting from the vertical short-period recordings.


ISSN: 0037-1106
EISSN: 1943-3573
Coden: BSSAAP
Serial Title: Bulletin of the Seismological Society of America
Serial Volume: 95
Serial Issue: 2
Title: Local and duration magnitudes in northwestern Italy, and seismic moment versus magnitude relationships
Affiliation: Istituto Nazionale di Geofisica e Vulcanologia, Milan, Italy
Pages: 592-604
Published: 200504
Text Language: English
Publisher: Seismological Society of America, Berkeley, CA, United States
References: 29
Accession Number: 2005-047926
Categories: Seismology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 3 tables, sketch map
N44°00'00" - N45°00'00", E07°00'00" - E11°00'00"
Secondary Affiliation: University of Genoa, ITA, Italy
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute. Abstract, Copyright, Seismological Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 200517
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