Presented to the Induced Seismicity Consortium, USC 2013

Stephen Holtkamp

Michael BrudzinskiBrian Currie

Miami University, Oxford OHDepartment of Geology and Environmental Earth Science

Template Matching to Characterize Induced Seismic Sequences without Local Seismic Networks

Youngstown Earthquakes - ODNR11 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.

Induced Seismic SequencesThe “proximity test” is most often used as

evidenceWhile 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)

Template Matching ProcedureIntroduction: What’s in a seismogram?

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Even small changes in the source location or focal mechanism will result in different recorded seismograms throughout the network.

Template Matching Procedure

Template Matching Procedure

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Template Matching Procedure

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Template Matching ProcedureCorrelate for Long Periods of Time

e.g., for one day, cross correlation technique shows:(Nov 20, 2011)

Template Matching ProcedureDo 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

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

Template Matching ResultsBest results from processing two years of data.

Template Matching Results282 Earthquakes (25x as many than with traditional techniques)

Starts two weeks after pumping starts

Evidence of Different Phases/Moving Source?Compute waveform interferogram

This gets us precise relative arrival times.

time

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

EQ Triggering Delay TimeEarthquake 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.

Template Matching RemarksOverall Requirements for template matching earthquakes

Quality seismometersLong periods of continuous dataStation spacing on the order of 50-150 km ok for broadband.

Can get us complete (but specific) catalog down to ~M1Any 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 foldSimilar results from my preliminary work in Alaska and MexicoCan be done without deploying costly and scientifically focused local network.

Also gives us ability to look backwards in time

We find >280 earthquakes in the Youngstown SequenceEarthquakes 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 activityCould 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

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.

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?

Why only this Well?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 hole3. Presense of pre-existing fractures/faults

1. Some oriented in a manner consistent with regional stress field,

and the M4 Earthquake

ODNR (2012)

Conceptual Model1. Fluids are being injected into basement rock that is faulted

with an orientation consistent with regional stress field.

Conceptual Model1. 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.

Evidence of Different Phases/Moving Source?Compute Inter-Event Correlation Matrix

Compares every event to every other event Similar events represented by warmer colors

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)

Small Earthquakes are tough to findE.g., these M<1 earthquakes are not clearly visible

Hypothetical Example: What if Youngstown events were all < M1.0

Small Earthquakes can to be stacked togetherWhen properly aligned and stacked, become easily seen

Hypothetical Example: What if Youngstown events were all < M1.0

Small Earthquakes need to be stacked togetherWhen 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