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On the extraction of microseismic ground motion from analog seismograms for the validation of ocean-climate models

Thomas Lecocq, Fabrice Ardhuin, Fabienne Collin and Thierry Camelbeeck
On the extraction of microseismic ground motion from analog seismograms for the validation of ocean-climate models
Seismological Research Letters (April 2020) 91 (3): 1518-1530

Abstract

We report on a pilot demonstration of the usefulness of analog seismograms to improve the database of ocean storms before the 1980s by providing additional data for the quantitative validation of ocean wave modeling, in particular for extreme events. We present a method for automatic digitization of paper seismograms to extract microseismic ground-motion periods and amplitudes. Each minute of the original paper records is scanned and vectorized. The amplitudes are calibrated based on the original metadata taken from official bulletins. The digitized time series is processed to extract power spectral densities, which are compared with modeled microseisms levels computed using a numerical ocean wave model. As a case study, we focus on one month of data recorded at the Royal Observatory of Belgium (ROB) from January to February 1953, around the "Big Flood" event, a tragic storm surge that flooded the lowlands of England, the Netherlands, and Belgium on 1 February 1953. The reconstructed spectrograms for the three components of ground motion show clear storm signatures that we relate to specific sources in the North Atlantic Ocean. However, our models of the Big Flood event based on these data do not result in the expected amplitudes as modeled compared to the observational data when the storm reached its maximum in the southern North Sea. We suggest that the source of microseisms recorded at ROB is related to the primary microseism generated in the North Sea, at periods of 7-8 s. Other discrepancies identified suggest small modifications of the source locations or energy. Reconstructed horizontal and vertical ground motions are coherent. This is a good news for the purpose of present-day analyses of constructing twentieth century ocean-climate models, especially as during much of that time only horizontal seismographs were installed at observatories.


ISSN: 0895-0695
EISSN: 1938-2057
Serial Title: Seismological Research Letters
Serial Volume: 91
Serial Issue: 3
Title: On the extraction of microseismic ground motion from analog seismograms for the validation of ocean-climate models
Affiliation: Royal Observatory of Belgium, Brussels, Belgium
Pages: 1518-1530
Published: 20200401
Text Language: English
Publisher: Seismological Society of America, El Cerrito, CA, United States
References: 91
Accession Number: 2020-039413
Categories: Seismology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table
N51°00'00" - N61°10'00", W04°00'00" - E11°00'00"
N49°30'00" - N51°30'00", E02°30'00" - E06°30'00"
Secondary Affiliation: University of Brest, FRA, France
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2022, American Geosciences Institute. Abstract, Copyright, Seismological Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 202025
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