1. Presented to the Induced Seismicity Consortium, USC 2013 Stephen Holtkamp Michael Brudzinski Brian Currie Miami University, Oxford OH Department of Geology and Environmental Earth Science

2. Youngstown Earthquakes - ODNR 11 Recorded seismic events in Youngstown, OH by the ODNR Traditional seismic techniques Magnitude down to 2.1 Not a good characterization of seismicity. Potentially induced by a wastewater injection well Emergency local network of seismometers deployed in Dec. to test this hypothesis Events passed “proximity test” – enough to shut down operations.

3. Induced Seismic Sequences The “proximity test” is most often used as evidence While it is good evidence, hardly constitutes proof So, we need something else: We can use advanced seismic techniques Multiple station template matching (or network matched filter)

4. Template Matching Procedure Introduction: What’s in a seismogram? SourcePath * Receiver * Seismogram= Mo. t *,, * t Voltage = Even small changes in the source location or focal mechanism will result in different recorded seismograms throughout the network.

5. Template Matching Procedure

6. Time (seconds) 0 40 12 Cross Correlation Coefficient 0

7. Template Matching Procedure Time (seconds) 0 40 12 Cross Correlation Coefficient 0

8. Template Matching Procedure Correlate for Long Periods of Time e.g., for one day, cross correlation technique shows: (Nov 20, 2011)

9. Template Matching Procedure Do this for Long Periods of Time e.g., for one day, cross correlation technique shows: (Nov 20, 2011) Want to establish a detection threshold ~=one false positive per year

10. Template Matching Advantage Advantage: Correlation value is not a function of background noise Best technique for finding earthquakes (or any other discrete seismic signals) during “noisy” periods Cultural noise Heavy Industrial Activity Large Earthquakes Volcanic Eruptions

11. Template Matching Results Best results from processing two years of data.

12. Template Matching Results 282 Earthquakes (25x as many than with traditional techniques) Starts two weeks after pumping starts

13. Evidence of Different Phases/Moving Source? Compute waveform interferogram This gets us precise relative arrival times. time

14. Evidence of Different Phases/Moving Source? Locate earthquakes relative to a well located event. Accurate enough to see very small changes in source location. Overall migration velocity 1-2 km/year Events collapse to WSW trend For well constrained EQ’s Events start near well Migrate WSW over 1 year. There may be a parallel trend

15. EQ Triggering Delay Time Earthquake activity and pumping are well correlated with 1- and 4- day lag times (for each template respectively) Time it takes for fluid pressure to reach earthquake source region. ~0.3 km/day for both families here.

16. Template Matching Remarks Overall Requirements for template matching earthquakes Quality seismometers Long periods of continuous data Station spacing on the order of 50-150 km ok for broadband. Can get us complete (but specific) catalog down to ~M1 Any visible earthquake Not necessarily even located, just record some arrivals above background noise. Template matching can lower completeness threshold by ~1 Magnitude level and increase detected events ~10-20 fold Similar results from my preliminary work in Alaska and Mexico Can be done without deploying costly and scientifically focused local network. Also gives us ability to look backwards in time

17. We find >280 earthquakes in the Youngstown Sequence Earthquakes appear to be directly caused by the Northstar Wastewater injection well. We can go well beyond the standard “proximity test.” We find evidence that new areas of the fault were being opened up for potential earthquake activity Could potentially keep increasing the earthquake size Template matching provides an excellent method to test potential cases of induces seismicity. Or for enhanced detection of any other seismic signal Conclusions

18. Thank You! Acknowledgements Funding provided by M. Brudzisnki’s NSF CAREER Grant EAR-0847688 Special thanks to B. Currie for working with earthquake seismologists and providing many insightful discussions. The ODNR for compiling and publishing information critical to our conclusions. Also for inviting us to the OhioSeis meeting, Columbus OH (Aug. 15, 2012), and hosting an informative discussion.

19. There are 10’s of thousands of injection wells in the U.S. Does anything set this well apart? 1. The well was drilled ~200 ft into Precambrian crystalline basement. 2. Base of well was finished open hole ODNR (2012) Why only this Well?

20. There are 10’s of thousands of injection wells in the U.S. Does anything set this well apart? 1. The well was drilled ~200 ft into Precambrian crystalline basement. 2. Base of well was finished open hole 3. Presense of pre-existing fractures/faults 1. Some oriented in a manner consistent with regional stress field, and the M4 Earthquake ODNR (2012)

21. Conceptual Model 1. Fluids are being injected into basement rock that is faulted with an orientation consistent with regional stress field.

22. Conceptual Model 1. Fluids are being injected into basement rock that is faulted with an orientation consistent with regional stress field. 2. Pore fluid pressure in the fault increases, allowing EQ’s to occur. 3. Fault slip may allow fluid to infiltrate new areas of the fault. 1. This increases fault area available for future earthquakes.

23. Evidence of Different Phases/Moving Source? Compute Inter-Event Correlation Matrix Compares every event to every other event Similar events represented by warmer colors

24. Example: Using small EQ as template Making a template from M~1 Earthquake The template is well matched with several larger earthquakes Gives us location January 11, 2011 (First earthquake in sequence)

25. Small Earthquakes are tough to find E.g., these M<1 earthquakes are not clearly visible Hypothetical Example: What if Youngstown events were all < M1.0

26. Small Earthquakes can to be stacked together When properly aligned and stacked, become easily seen Hypothetical Example: What if Youngstown events were all < M1.0

27. Small Earthquakes need to be stacked together When properly aligned and stacked, become easily seen M<1.0 Stacks are almost as good as M2-4 Events (!) Hypothetical Example: What if Youngstown events were all < M1.0 M<1.0 M>2.0