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TitleRemote dynamic triggering of earthquakes in three unconventional Canadian hydrocarbon regions based on a multiple-station matched-filter approach
AuthorWang, B; Harrington, R M; Liu, Y; Kao, HORCID logo; Yu, H
SourceBulletin of the Seismological Society of America vol. 109, no. 1, 2018 p. 372-386,
Alt SeriesNatural Resources Canada, Contribution Series 20180220
PublisherSeismological Society of America (SSA)
Mediapaper; on-line; digital
File formatpdf; html
ProvinceBritish Columbia; Alberta; Northwest Territories; New Brunswick
NTS93N; 93O; 93P; 94A; 94B; 94C; 94F; 94G; 94H; 94I; 94J; 94K; 94N; 94O; 94P; 95A; 95B; 95C; 96C; 96D; 96E; 96F; 21A; 21B; 21G; 21H; 21I; 21J
Lat/Long WENS-125.0000 -119.0000 61.0000 55.0000
Lat/Long WENS-128.0000 -125.0000 66.0000 64.0000
Lat/Long WENS -67.0000 -64.0000 47.0000 44.0000
Subjectsgeophysics; environmental geology; fossil fuels; structural geology; earthquakes; seismicity; seismic waves; seismic velocities; earthquake catalogues; petroleum resources; hydrocarbons; hydrocarbon recovery; seismological network; statistical analyses; stress analyses; bedrock geology; structural features; faults; lithology; sedimentary rocks; shales; pore pressures; modelling; basins; monitoring
Illustrationslocation maps; focal mechanisms; spectra; time series; histograms; plots; tables
ProgramEnvironmental Geoscience Shale Gas - induced seismicity
Released2018 12 04
AbstractWe investigate the occurrence of remote dynamic triggering in three Canadian unconventional hydrocarbon regions where recent fluid injection activity is correlated with increasing numbers of earthquakes. We select mainshocks with an estimated local peak ground velocity exceeding 0:01 cm=s occurring between 2013 and 2015, when station coverage was increased to monitor injection activity. A twofold approach, using continuous waveform data and an enhanced earthquake catalog created using a multiple-station matched-filter detection algorithm, suggests that remote dynamic triggering occurs at all three regions. The waveform-based approach shows evidence for direct triggering in the surface wavetrain of the mainshock, as well as directly afterward in the coda. The enhanced catalog approach shows qualitative increases in earthquake rates at all three regions that are both immediate, and in some cases, sustained over 10-day time windows and are corroborated with two types of statistical tests: a p-value test to quantify the statistical significance of earthquake rate change following a stressing event and an interevent time test that provides a statistical measure of changes in seismicity rates. The occurrence of both direct and delayed triggering following transient stress perturbations of < 10 kPa in all three regions suggests that local faults may remain critically stressed over periods similar to the time frame of our study (?2 yrs) or longer, potentially due to high pore pressures maintained in tight shale formations following injection. The results interpreted in the context of injection history and recent poroelastic modeling results may have implications for the mechanisms of remote triggering. Namely, triggering via poroelastic stresses may provide a unifying mechanism that can explain both delayed and immediate triggering observations.
Electronic Supplement: Figures showing the waveforms and correlation matrix for the 200 template events in British Columbia and Alberta (BCAB) used in the multiple-station matched-filter (MMF) approach, example of an earthquake family in BCAB, detection accuracy of the MMF algorithm as a function of the mean absolute deviation value, Pc?sum-value and Pri-value as a function of the time window used to calculate changes in seismicity rates, focal mechanism solutions for events occurring from 2001 to 2005 in the BCAB regions with M > 4, cumulative energy density of triggering mainshocks, tables with information of the remote mainshocks and the reference numbers in the main article, number of directly triggered earthquakes for each of the regions studied here, and the maximum observed transient stress from all of the mainshocks.
Summary(Plain Language Summary, not published)
We examine the local earthquake occurrence rates in 3 major unconventional hydrocarbon regions (northeast British Columbia and western Alberta, Northwest Territories, and New Brunswick). We found that the rate increases after the occurrence of large earthquakes that were located far away from these three regions. Our observations suggest that the passage of large-amplitude surface waves due to distant events can generate stress disturbances equivalent to tidal stress and are large enough to trigger local earthquakes (which is termed 'remote triggering'). Two different modes of remote triggering were observed: immediate triggering and delayed triggering. One important implication of our study is that local faults in the three regions are very close to the critical state, such that even a very small amount of stress disturbance can induce local earthquakes.

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