Investigating Time Dependent Velocity Structure in the Shallow Subsurface of the Raton Basin

Session: Advances in Seismic Interferometry: Theory, Computation and Applications [Poster]
Type: Poster
Date: 4/30/2020
Time: 08:00 AM
Room: Ballroom
Description: 

The Raton basin is an active coal bed methane field encompassing an ~3,500 km³ area located between the Rocky Mountains and the Great Plains. Coalbed methane production and associated wastewater injection has been occurring in the basin for the past ~20 years. The majority of wastewater is injected into basin sediments at depths of ~1.2-2.8 km. However, production occurs at shallower depths, ~0.2-1.8 km. Recent studies have found significant increases in earthquake frequency and magnitude and have documented changes in spatiotemporal patterns of seismicity related to wastewater injection. Fractional changes in seismic velocity structure through time, known as dv/v, have been attributed to several societally important upper crustal processes, such as earthquakes, hydrologic cycling and geothermal reservoir fluctuations. Here we examine the extent to which variations in gas field production and wastewater injection, natural hydrologic cycles and transient stresses due to earthquakes perturb dv/v in the shallow subsurface of the Raton Basin. Data for this project comes from 8 broadband three component seismometers spaced ~15-25 km apart in operation since 2016 and a nodal deployment of 90 5 Hz seismometers spaced ~2-5 km apart which recorded one month of data during the summer of 2018. We utilize the python software package MSNoise to compute cross correlations of seismic ambient noise and measure dv/v with the moving window cross spectrum technique. Within the frequency band 0.5-2 Hz, channel averaged dv/v results from the broadband stations over the time period between Sept. 2016 to Nov. 2019 show an overall ~0.1% decrease in the southern portion of the basin. This trend is absent in the northern part of the basin. We aim to understand the origins and regionalization of this long term dv/v decrease and investigate short term variations in dv/v in more detail with nodal data.

Presenting Author: Justin Wilgus

Authors