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Understanding Controls on Maximum Induced Earthquake Magnitudes

Session: Mechanisms of Induced Seismicity: Pressure Diffusion, Elastic Stressing and Aseismic Slip I

Type: Oral

Date: 4/19/2021

Presentation Time: 03:00 PM Pacific

Description: 

Injection of fluids into the subsurface for industrial operations, such as wastewater disposal, geothermal energy production, and carbon sequestration is known to cause earthquakes. Forecasts of the hazard associated with such induced seismicity often require estimates of the maximum possible magnitude (M_max) that may occur near a given site. Scaling relationships suggest that maximum magnitudes or expected numbers of earthquakes are related to the volume of fluid injected into the subsurface; however, notable induced events such as the M5.5 2017 Pohang, South Korea event defy this scaling. To understand the controls on M_max, we perform a suite of 3-D physics-based earthquake simulations with rate- and state-dependent friction, where we systematically vary the area of the pressurized region and the amplitude of the initial homogeneous or heterogeneous shear stress. Using the resulting catalogs, we explore the conditions that result in pressure-controlled ruptures (confined within the pressurized area) versus runaway ruptures that extend well outside the pressurized zone. We find that proposed empirical scaling laws correctly predict M_max when shear stresses are farther from failure (<=90% of maximum shear stress) and for short wavelength, high amplitude stress fields. Runaway ruptures are observed for higher initial shear stresses and smoother stress fields without low stress barriers to impede rupture. In these cases, runaway ruptures occur early after the onset of injection and are rarely proceeded by extensive foreshock activity.

Prepared by LLNL under Contract DE-AC52-07NA27344.

Presenting Author: Kayla Kroll

Student Presenter: No

Authors