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Magnitude Thresholds to Evaluate the Damage From Induced-Seismicity Earthquakes

Session: Seismic Hazard Analysis for Critical Infrastructure [Poster]

Type: Poster

Date: 4/19/2021

Presentation Time: 03:45 PM Pacific

Description: 

It is common practice in seismic hazard analysis to only consider ground motions from earthquakes with magnitudes greater than M5 based on the assumption that smaller earthquakes cannot damage engineered structures. We are evaluating this assumption for the case of small-to-moderate magnitude (M3-M4) earthquakes occurring at shallow depths from induced seismicity associated with wastewater injections and hydraulic fracturing. Due to the shallow depths, the distances from the source to the site can be small (just a few km), and with the steep distance attenuation, the median short-period ground motions at 3 km distance from induced earthquakes can be significant. The combination of the increased median ground motion at short distances and the increased rate of earthquakes brings into question the assumption that earthquakes less than M5 cannot cause damage to earth structures.

We are currently evaluating the potential effects of induced-seismicity ground motions on the seismic performance of dykes, focusing on identifying the minimum magnitude that can cause damage. We selected ground motions with the frequency content of induced-seismicity ground motions and scaled them to have intensity measures (IM) that represent the aleatory variability. The selected ground motions are then used in dynamic analyses that consider analytical methods and advanced numerical modeling. The analytical methods relied on the transfer function model proposed by Hale (2020) and the stick-slip model proposed by Rathje and Bray (2000). The advanced numerical analyses were performed with the software FLAC and nonlinear constitutive models. For dykes with yield accelerations of 0.1g, our preliminary results show that the earthquake magnitude that can cause significant deformation (> 10 cm) is between M3.5 to M4.0 for a rupture distance of 3 km using the ground motions with the spectral content from induced earthquakes at short distances. In addition, the results using FLAC are more conservative, which is associated with the assumptions in analytical models.

Presenting Author: Jorge E. Macedo

Student Presenter: No

Authors