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Characterization of an Earthquake Sequence Triggered by Hydraulic Fracturing in Harrison County, Ohio by Paul A

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Characterization of an Earthquake Sequence Triggered by Hydraulic Fracturing in Harrison County, Ohio by Paul A ○E Characterization of an Earthquake Sequence Triggered by Hydraulic Fracturing in Harrison County, Ohio by Paul A. Friberg, Glenda M. Besana-Ostman, and Ilya Dricker Online Material: Tables of hypoinverse earthquake locations ment to this article). Notably, the waveforms at TA O53A and velocity models. of each of the earthquakes were remarkably similar (Fig. 1) suggesting that all seismic events were from the same source. INTRODUCTION Initial locations of the earthquakes were calculated by man- ually picking P and S arrivals using SeisAn software (Havskov and To extract oil and gas in tight shale formations, hydraulic Ottemöller, 1999)andviaHYPOCENTERlocationalgorithm fracturing is used to stimulate fracture growth and increase per- (Lienert et al.,1986; Lienert and Havskov, 1995). We used a regional 1D velocity model, herein called “NE Ohio” velocity meability. Typically, low (−3:0 to 0.0 M w) magnitude earth- quakes are produced during hydraulic fracturing (Maxwell model (Hansen and Ruff, 2003; Kim, 2013)withaV P=V S et al., 2002, 2009). In a few cases, however, hydraulic fracturing of 1.73 (Ⓔ Table S2). The initial locations of the earthquakes has been linked to widely observed larger, so-called positive were widely distributed laterally and vertically and showed no magnitude, earthquakes. Examples include earthquakes felt by pronounced clustering. Moment magnitudes for each of the the general population in such areas as Blackpool, England, earthquakes were determined using SeisAn’s spectral long-period displacement fitting algorithm (Ottemöller and Havskov, 2003) M L 2.3 (de Pater and Baisch, 2011), Horn River Basin, Can- using the average M of the five closest TA stations. ada, M L 3.8 (British Colombia Oil and Gas Commission w All 10 earthquakes were then relocated using the NE Ohio [BCOGC], 2012), and Oklahoma M L 2.9 (Holland, 2011, 2013) and more recently in Ohio (Skoumal, 2014). In this pa- velocity model and HYPOINVERSE (Klein, 2007) to obtain per, we show the first evidence of positive magnitude earth- an improved uncertainty ellipsoid and improved precision in quakes on a previously unmapped fault in Harrison County, starting location (Fig. 2b). The earthquakes had an average root Ohio, that can be related to a hydraulic fracture operation. mean square (rms) of 0.062 s, average vertical uncertainty of 732 m, and average horizontal uncertainty of 432 m. REGIONALLY LOCATED EVENTS Using manual phase picks to relocate the earthquakes with the double-difference algorithm HypoDD (Waldhauser and A series of six earthquakes were located by the Array Network Ellsworth, 2000; Waldhauser, 2001) showed no pronounced Facility regional seismic network using the Incorporated structure responsible for the sequence. Employing waveform Research Institutions for Seismology (IRIS) EarthScope cross-correlation techniques around the phase arrivals (Schaff, Transportable Array (TA) stations in Ohio on 2 October 2008; Schaff and Waldhauser, 2010) along with the manual 2013. These earthquakes were located south of Clendening phase picks, however, helped to better constrain the relative lo- Lake in Harrison County near the town of Uhrichsville, Ohio, cations (Fig. 2b). After HypoDD relocations on the combined and included two M w 2.0 events. This series of earthquakes was data, the seismicity defined roughly a linear pattern oriented followed by four more events with M w 1.7–2.2 from 3 to 19 east–west as the possible source of the earthquakes with depth October. There were no felt reports for any of these earthquakes. ranges of 3.8–4.0 km. The HypoDD relative uncertainty de- Upon inspection of the OhioSeis seismic network catalog (Han- rived from the singular value decomposition (SVD) option sen and Ruff, 2003) and other available historical catalogs in the was 84 m longitudinal, 107 m latitudinal, and 115 m region (Stover and Coffman, 1993), this series of earthquakes is vertical. Unfortunately, first-motion focal mechanisms could the first known seismic occurrence in the region. not be obtained for any of the earthquakes due to noisy data The closest station to the earthquakes was the IRIS at more distant stations and inadequate station distribution. EarthScope TA O53A station located within 2–3 km of the To better constrain the absolute location of the regional earthquakes based on S–P times of 0:66 0:02 s for all 10 cluster, we performed back-azimuth analysis on three- earthquakes (Ⓔ Table S1, available in the electronic supple- component data of TA O53A station using the method of doi: 10.1785/0220140127 Seismological Research Letters Volume 85, Number 6 November/December 2014 1 ▴ Figure 1. Normalized P-wave aligned waveforms from O53A’s (a) vertical component, BHZ, and (b) one horizontal component, BHE, channels for 10 earthquakes located using Transportable Array (TA) stations. 2 Seismological Research Letters Volume 85, Number 6 November/December 2014 (a) Roberts et al. (1989). The back azimuths were computed based 42° TA-L53A on 1 s- and 2 s window measurements around the P arrival for each earthquake. The analysis showed that all of the earth- quakes were on average at 174° north azimuth 14° from TA-M52A Cleveland TA-M53A TA O53A (Fig. 2a), which is inconsistent with the majority TA-M50A TA-M51A of the HYPOINVERSE locations that scatter about the TA Ohio Pennsylvania Akron Youngstown O53A station. This inconsistency indicates a need for a better 41° TA-N54A TA-N51A modeling of the velocity structure in the region and a need for TA-N52A TA-N53A TA-N50A station corrections. Pittsburgh CROSS-CORRELATION TEMPLATE EVENT US-ACSO TA-O53A TA-O54A TA-O51A TA-O52A DETECTIONS 40° Columbus The EarthScope TA stations were primarily deployed to study TA-P52A TA-P54A Morgantown deep regional structures across the United States continental TA-P51A US-P53A region. Hence, the next nearest TA stations to O53A are about West Virginia 50–120 km away. Thus, their records showed poor or no visible 0 50 signals for small-sized earthquakes located outside the 5 km 39° -83° -82° -81° -80° proximity. Therefore, to determine if there are other possible earthquakes or earthquake sequence in this region prior to the (b) 2 October cluster, the study focused on the O53A station data- set in which we applied a template event cross-correlation sig- 40°15′ TA.O53A OHH3 nal detection technique (Gibbons and Ringdal, 2006; Holland, 4 6 2013; van der Elst et al., 2013; Meng and Peng, 2014) to find 8 2 lower magnitude earthquakes. The 2 October 10:06 UTC M w 2.0 earthquake was used as a template event due to its high 40°14′ 5 3 R4 R3R2 signal-to-noise ratio (SNR) at the station. The template was 10 built from a 5.0 s window of the vertical component that in- 9 cludes the full waveform: pre-P noise, P arrival, S arrival, and 1 S-coda portion of the earthquake. The event template was fil- 40°13′ tered from 1.0 to 5.0 Hz and then 10% cosine tapered. Because 7 the template includes the full waveform, matching waveform OHH4 detections can be assumed to be from earthquakes that are very OHH2 close to the template event in location and focal mechanisms 40°12′ and therefore are likely to be on the same fault. The template was applied to over a month of data (1 Sep- tember to 2 October) prior to the first locatable earthquakes. ≥ 40°11′ With a detection threshold 0:60 for the normalized cross- correlation coefficient, this process produced 1072 earthquake 1 km signal detections as shown in Figure 3a. Upon visual inspection, OHH1 however, we observed that around 15% of the detections were 40°10′ false and some earthquakes with a low SNR were barely resolv- -81°16′ -81°15′ -81°14′ -81°13′ -81°12′ -81°11′ able. To improve the event identification, the detection thresh- old of 0.70 was used, which produced 698 detections with a ▴ Figure 2. (a) The location of TA stations deployed in Ohio with significant reduction in false detections. In this second set of the TA stations used (red inverted triangles) in locating the 10 detected waveforms, however, accurate picks for both P- and earthquakes observed from 2 to 19 October. The small rectangle S-phase arrivals were still not possible. A detection threshold around O53A is the region expanded in map (b). (b) The TA station of 0.85 yielded 298 matches with zero false detections (Fig. 3b), O53A (red triangle) and four portable station locations (green tri- whereas lower thresholds resulted in a progressively greater angles). The 10 regional earthquakes located by HYPOINVERSE number of false detections. The earliest among these 298 iden- (numbered blue error ellipses) are also plotted together with their tified waveforms were observed on 8 September at 06:21 UTC, final locations using HypoDD (solid blue circles). The three hori- whereas the greatest density of detections per time interval oc- zontal wells stimulated during the early and late part of 2013 are curred between 1 October (08:41 UTC) and 2 October (23:59 also shown marked at the toe of the horizontal section by the la- UTC). During this 39-h period, a total 190 earthquakes were bels R3, R2, and R4. The map projection of their paths is shown as identified whereas the largest number of detections in a single red, blue, and green lines, respectively. day of 120 occurred on 2 October. Not surprisingly, waveforms Seismological Research Letters Volume 85, Number 6 November/December 2014 3 (a) (b) Harrison County Ohio Seismicity 7 September -14 December, 2013 3 21 09/07/2013 07:54UTC 10/06/2013 13:18UTC cm Injection Start Injection Stop ⋅ 20 ) 2 W 19 M 18 1 17 16 Moment Magnitude ( 0 5000 15 (Cumulative Seismic Moment), dyn 4000 10 3000 2000 Log 1000-1 14 BBL per hr 0 10 20 30 40 50 60 70 80 90 100 Days after injection start (7 September, 2013) ▴ Figure 3.
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