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Time-Dependent Earthquake Forecasts With Pre-Existing Populations of Faults: Application to the Groningen Gas Field, the Netherland

Description: 

The Groningen gas field, one of the largest producing onshore gas fields in Europe, is often considered a model test site for induced seismicity. This is due to the open availability of production and detailed structural and field parameters, together with an outstanding effort to monitor shallow, low magnitude seismicity from surface and borehole arrays. A key observation at Groningen is that induced seismicity at depths of about 3 km started with a delay of almost 40 years after the start of production and long after peak production rates were realised. This can be attributed to the fact that the shallow Rotliegend sediments at 3 km depth and pre-existing fault distributions are subcritically stressed. Common seismicity models such as Rate and State (RS) or ETAS do not usually take into account pre-existing fault distributions and pre-stress models.

In this study, we use a recently developed physics-based seismicity model (TDSR) that assumes pre-existing populations of faults that respond to changes in Coulomb stress. In contrast to the traditional Coulomb Failure (CF) model, which assumes instantaneous triggering when stress exceeds a threshold value, the new model replaces instantaneous triggering with an average time to failure that depends exponentially on the absolute stress value. In the new model, the predictions of both CF and RS are special cases for constrained initial and boundary conditions. It is more general and flexible to consider, for example, subcritical initial stress states as commonly assumed for induced or intraplate seismicity. We estimate the pre-stress distribution at Groningen based on the background stress field and the existing fault structure. Using this and the temporal evolution of the 2D stress field in the reservoir, we show that the delayed onset, the peak seismicity rate in 2013-2015 and the decline in observed seismicity today are well explained.

Session: New Insights into the Development, Testing and Communication of Seismicity Forecasts - I

Type: Oral

Date: 5/2/2024

Presentation Time: 04:45 PM (local time)

Presenting Author: Torsten

Student Presenter: No

Invited Presentation: 

Authors