Seismicity of Bull Shoals Lake Area of Missouri and Arkansas

Date: 4/26/2019

Time: 06:00 PM

Room: Fifth Avenue

Northern Arkansas, historically aseismic, has seen an increase in the seismicity in the vicinity of Bull Shoals Lake area of Arkansas and Missouri since 2017. It is hypothesized that: 1) an intense rainfall event, 2) the rate at which the lake filled over a short timeframe, and 3) nearby geologic structural components were the cause this seismicity. Since April, 2017, there have been 61 seismic events. The main event, a M3.6, occurred on June 11, 2017. Prior to this sequence, the area reported only 18 events which have occurred over the past 90 years. The moment tensor indicated a strike slip normal fault earthquake at a depth of 6.0 km. This investigation revealed that the region received over 20 inches of rain over two month period in an area which normally receives an average rainfall of 42 inches and that the lake level increased more than 37 feet over a period of 48 days. The nearby structural component, the Ponca Lineament (northeast-southwest) extension has been projected to run through this seismic cluster. Previous studies (Snow, 1972, Talwani, 1976, Talwani, et al, 2007) have demonstrated that pore pressure diffusion is associated with the buildup of fluid pressures and the onset of seismicity. Talwani’s study (90+ induced seismicity case histories) determined that the hydraulic diffusivity (“C”) value of fractures associated with seismicity to lie between 0.1 and 10 meters² per second (referred to as the seismogenic permeability k_s). For the Bull Shoals study area, based on preliminary calculations, it is proposed that the change in the pore pressure/diffusion (hydraulic diffusivity or “C”) is on the order of about 0.2 meters² per second.

Presenting Author: Martha T. Kopper

Authors