Webinar cycle in Hydrogeology and geochemistry
HYDROGEOLOGY GROUP (Associated Unit CSIC-UPC, Barcelona)
Date: Thursday, 21 October 2021
Starting time: 12:15pm (Central European Time)
Duration: 1h
Guest Speaker: Haiqing Wu, PhD Student
Title: Uncertainty analysis on the potential triggering mechanisms of the Pohang Mw5.5 earthquake
live in: https://meet.google.com/snb-qdkn-eex (free of charge)
Abstract:
The Pohang earthquake not only is the largest seismic event induced by any enhanced geothermal system (EGS) project, but also is a typical post-injection induced event. Although it is now commonly accepted that the earthquake was induced by high-pressure hydraulic stimulation, the detailed triggering processes and mechanisms remain under debate. To shed light into them, we first make a comparative analysis on the relative likelihood of the existing in-situ stress states for the Pohang EGS site at depth, which present a wide range of values, based on the linear Mohr-Coulomb criterion. Accordingly, we propose two likely oblique-slip faulting patterns to analyze the problem of induced seismicity: a reverse faulting pattern with a strike-slip component (RF-S) and a strike-slip faulting pattern with a reverse component (SS-R). We then analytically evaluate the coupled hydro-mechanical responses in the quasi-expanding reservoir at the instance of the mainshock for both faulting patterns, and assess the induced seismicity potential. Parametric space analysis shows that the magnitude of in-situ stress and the friction coefficient are playing a more significant role in inducing a seismic event than Biot’s coefficient and the fault geometry. Probabilistic assessment shows that the SS-R faulting pattern is closer to the actual scenario than the RF-S case, the probabilities of inducing an earthquake Mw>3.0 and the Pohang earthquake for the former reach ∼14% and ∼10%, respectively. Thus, the most likely triggering mechanism for the Pohang earthquake is the reactivation of a critical strike-slip fault with a high dip angle due to the pore pressure buildup in the reservoir and its subsequent poroelastic stress. The closed form solutions facilitate the uncertainty analyses that involves multiple uncertain parameters, the methodology that applied in this work thus can be regarded as a routinely option for risk assessment of the geo-energy related projects.
Webinars will be recorded and made available one day after the talks in www.h2ogeo.upc.edu