On the Extraction of Microseismic Ground Motion from Analog Seismograms for the Validation of Ocean-Climate Models

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.

Spatiotemporal Correlation Analysis of Noise‐Derived Seismic Body Waves With Ocean Wave Climate and Microseism Sources

“…Instrumental observation of microseisms has an over‐century history and started much earlier than the modern observations of ocean waves and storms. It has been a long‐lasting effort for the seismological community to digitalize the historical analog seismograms (Bogiatzis & Ishii, 2016; Lecocq et al, 2020). Researchers expect that past seismic records can be used to recover undocumented historical ocean storms and wave climate (Ebeling, 2012; Lecocq et al, 2020).…”

Achievements and Prospects of Global Broadband Seismographic Networks After 30 Years of Continuous Geophysical Observations

“…One hurdle is that WWSSN seismograms were recorded on paper drums (Peterson & Hutt, 2014) which complicates analysis. However, advances in digitization of paper records (e.g., M. Wang et al., 2014) have started to be leveraged to extract historical microseism properties (Lecocq, Ardhuin, et al., 2020). Improvements in modeling of microseism source processes, verified through microseism observations made predominantly at GEOSCOPE and GSN stations, has increasingly facilitated validation of global wave hindcast estimates (Ardhuin et al., 2011; Kedar et al., 2008).…”

Monitoring extreme meteo-marine events in the Mediterranean area using the microseism (Medicane Apollo case study)

“…In addition, it is also possible to analyze extreme meteorological past events for which there are no directly available meteorological data. In fact, Lecocq et al 32 digitised old seismograms already proved their potential in providing useful information about the microseismic signal associated with oceanic storms.…”