Aftershock sequence of the 2011 Virginia earthquake derived from the dense AIDA array and backprojection

Journal Article · Sun Apr 01 00:00:00 EDT 2018 · Bulletin of the Seismological Society of America

DOI:https://doi.org/10.1785/0120180107· OSTI ID:1498767

Beskardes, Gungor Didem ^[1]; Wu, Qimin ^[2]; Hole, John A. ^[3]; Chapman, Martin C. ^[3]; Davenport, Kathy K. ^[4]; Brown, Larry D. ^[5]; Quiros, Diego A. ^[6]

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1. Virginia Polytechnic Inst. and State Univ. (Virginia Tech), Blacksburg, VA (United States); Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
2. Virginia Polytechnic Inst. and State Univ. (Virginia Tech), Blacksburg, VA (United States); Univ. of Oklahoma, Norman, OK (United States)
3. Virginia Polytechnic Inst. and State Univ. (Virginia Tech), Blacksburg, VA (United States)
4. Virginia Polytechnic Inst. and State Univ. (Virginia Tech), Blacksburg, VA (United States); Oregon State Univ., Corvallis, OR (United States)
5. Cornell Univ., Ithaca, NY (United States)
6. Cornell Univ., Ithaca, NY (United States); Baylor Univ., Waco, TX (United States)

After the 23 August 2011 Mineral, Virginia, earthquake, a temporary dense array (Aftershock Imaging with Dense Arrays (AIDA)) consisting of ~200 stations was deployed at 200-400 m spacing near the epicenter for 12 days. Backprojection of the data was used to automatically detect and locate aftershocks. The co-deployment of a traditional aftershock network of 36 stations at ~2-10 km spacing enables a quantitative comparison. The AIDA backprojection aftershock catalog is complete to magnitude -1.0 and includes events as small as M-1.8. For comparison, the traditional network was complete to M-0.3 for the same time period. The AIDA backprojection catalog observes the same major patterns of seismicity in the epicentral region, but additional details are illuminated. The primary zone of seismicity is not a single fault but is a tabular zone of multiple small faults, this zone has a subtle concave shape along strike and with depth, and a broader zone of new events is observed at shallow depth. In addition, a new separate, shallow cluster was detected and located to the east of the main aftershock zone. The addition of smaller events to the catalog did not change the b-value or the temporal decay constant, but illuminated spatial and temporal patterns. Both the b-value and temporal decay constant are different for 12 days than for 4 months and are different at < 3km depth than at greater depth. Very low b-value, especially at greater depth, is consistent with observed very high stress drops. Conclusively, the results indicate the benefits of dense arrays and auto-detection by backprojection for aftershock studies. And finally, the reduced detection threshold and higher spatial resolution enabled the study of earthquake mechanisms and strain transfer at an unprecedented small scale.

• Research Organization: Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA)
• DOE Contract Number: AC04-94AL85000
• OSTI ID: 1498767
• Report Number(s): SAND2018-3486J; 662025
• Journal Information: Bulletin of the Seismological Society of America, Vol. 109
• Country of Publication: United States
• Language: English