Deliverable 2.4 Updated catalog and focal mechanism database
Martuganova, Evgeniia; Kettlety, Tom; Jerkins, A.; Kühn, N.; Langet, N.; Schweitzer, J.; Baptie, Brian; Dahl-Jensen, Trine; Asplet, J.; Voss, P.; Kendall, J. Michael; Barnhoorn, A.
Research report
Published version
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https://hdl.handle.net/11250/3171199Utgivelsesdato
2024-05Metadata
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- NGI report [224]
Sammendrag
This report describes updates to the North Sea seismicity event bulletin in which all earthquakes from databases of the countries bordering the North Sea are amalgamated into a single bulletin. This is the first dataset of its kind and makes up the most complete and homogeneous bulletin for the North Sea at the time. A comprehensive evaluation of the natural earthquake activity provides important information on the stress field and faulting mechanisms near the proposed reservoirs for carbon capture sequestration. The collected information is crucial for the understanding of the response of the reservoir and caprock to large-scale fluid injection. This deliverable describes the subsequent analysis comprised of event magnitudes, locations, and moment tensor inversion to derive source mechanisms.
SHARP’s North Sea earthquake bulletin is updated from the earlier produced bulletin presented in deliverable D2.1. The new bulletin comprises mostly the removal of explosion events and minor formatting issues and constitutes the most complete and - despite unresolved challenges - the most homogeneous representation of North Sea seismicity available to date. Two byproducts of the new bulletin are a catalogue consisting of prime information and a catalogue extended to a larger region as base for the seismic hazard analysis performed in WP 5. Furthermore, analyses are performed on different magnitude scales. The usage of different formulas and input data makes direct comparisons between magnitudes difficult, especially for the local magnitudes. An analysis is also performed to relocate events within the North Sea bulletin, making use of the abundance of the new compilation of phase information. Our effort now also includes collecting waveforms for events that occurred later than 1990 and had magnitudes larger than M 3.5, although quality control of these waveforms was not possible yet. Lastly, previously computed focal mechanisms are collected, and new moment tensors are calculated mainly for the larger magnitude events. We conclude that for many events, the number of available records as well as the data quality is not sufficient for reliable estimates of, e.g., source mechanisms.
Therefore, our main recommendation is to install more offshore seismic stations, particularly to add stations close to potential sources to increase the number of near-source observations and fill the azimuthal gaps in the station’s coverage to enable a more precise event location, event depth estimates and source mechanism analysis as well as enhance magnitude estimates. Especially with a view on the start up of CO2 injection and storage, it is important to establish a more reliable event analysis specifically for lower magnitude events that may potentially be induced events during operations. Without a dedicated plan to install a larger number of stations within the North Sea, a stable event analysis and derivation of estimates of stress orientations remain only possible for the largest magnitude event, not to mention the impossibility of a discrimination of natural and induced seismicity.
Serie
NGI-rapport;20210518-D2-4SHARP Storage;Deliverable 2.4