|Meeting||2012 Fall Meeting|
|Session||Induced Seismicity: Attribution and Triggering I|
|Authors||Rubinstein, J L*, US Geological Survey, Menlo Park, CA, USA Ellsworth, W L, US Geological Survey, Menlo Park, CA, USA McGarr, A, US Geological Survey, Menlo Park, CA, USA|
|Index Terms||Earthquake interaction, forecasting, and prediction |
The occurrence of an earthquake of magnitude (M) 5.3 near Trinidad, CO, on 23 August 2011 renewed interest in the possibility that an earthquake sequence in this region that began in August 2001 is the result of industrial activities. Our investigation of this seismicity, in the Raton Basin of northern New Mexico and southern Colorado, led us to conclude that the majority, if not all of the earthquakes since August 2001 have been triggered by the deep injection of wastewater related to the production of natural gas from the coal-bed methane field here. The evidence that this earthquake sequence was triggered by wastewater injection is threefold. First, there was a marked increase in seismicity shortly after major fluid injection began in the Raton Basin. From 1970 through July of 2001, there were five earthquakes of magnitude 3 and larger located in the Raton Basin. In the subsequent 10 years from August of 2001 through the end of 2011, there were 95 earthquakes of magnitude 3 and larger. The statistical likelihood of this rate increase occurring naturally was determined to be 0.01%. Second, the vast majority of the seismicity is located close (within 5km) to active disposal wells in this region. Additionally, this seismicity is primarily shallow, ranging in depth between 2 and 8 km, with the shallowest seismicity occurring within 500 m depth of the injection intervals. Finally, these wells have injected exceptionally high volumes of wastewater. The 23 August 2011 M5.3 earthquake, located adjacent to two high-volume disposal wells, is the largest earthquake to date for which there is compelling evidence of triggering by fluid injection activities; indeed, these two nearly-co-located wells injected about 4.9 million cubic meters of wastewater during the period leading up to the M5.3 earthquake, more than 7 times as much as the disposal well at the Rocky Mountain Arsenal that caused damaging earthquakes in the Denver, CO, region in the 1960s. Much of the seismicity since 2001 falls on a 15km-long, NE-trending lineation of seismicity dipping steeply to the SE. The focal mechanisms of the largest earthquakes since mid-2001 are consistent with both the direction of the seismicity lineation and the regional tectonic regime of east-west extension centered on the Rio Grande rift.
Cite as: Author(s) (2012), Title, Abstract S34A-02 presented at 2012 Fall Meeting, AGU, San Francisco, Calif., 3-7 Dec.