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Repeating Earthquakes Olivier Lengliné - IPGS Strasbourg Cargese school

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Please interrupt Questions / remarks

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1 – Review of Repeating earthquake observations & interpretations 2 – Two examples of application

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Observations - Waveforms Nadeau & Johnson, 1998

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Parkfield, California – Mw6.0 USGS Bakun et al., 2005 De Bilt, The Netherlands

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Uchida et al., 2012 Time (s) Off Kamaishi, Japan – M4.9

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Chen et al., 2008 Chihshang fault, Taiwan

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Time (s) 9 events 13 events 19 events Soultz-Sous-Forêts geothermal reservoir, France BRGM

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San-Andreas Fault Schaff & Beroza, 1998 Rubinstein et al., 2012

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u(t) = Source * Path * Station

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Station is the same Change in medium property, [e.g Poupinet et al., 1984] Change in source properties, [e.g. Lengliné & Got, 2011]

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Poupinet et al., 1984 Lengliné and Got, 2011 Directivity Velocity variations

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u(t) = Source * Path * Station Station the same Change in medium property, [e.g Poupinet et al., 1984] Change in source properties, [e.g. Lengliné & Got, 2011] ! Homogeneous medium waveform similarity

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Observations - Locations Waldhauser et al., 2004

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Murray & Langbein, 2006 Parkfield

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Off Kamaishi Okada et al., 2002 Relative moment released normalized by each maximum value Moment release distribution

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Earthquake relative relocation Uncertainties P-wave picks Uncertainties of the velocity model

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Earthquake relative relocation Uncertainties P-wave picks Uncertainties of the velocity model More precise data: time delays estimated from cross-correlation Ray geometry – rotation Do not correct absolute position

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Earthquake relative relocation Uncertainties P-wave picks Uncertainties of the velocity model More precise data: time delays estimated from cross-correlation Ray geometry – rotation Do not correct absolute position From cross-correlation centroid location Got et al., 1994 Waldhauser & Ellsworth, 2000

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Earthquake relative relocation Uncertainties P-wave picks Uncertainties of the velocity model More precise data: time delays estimated from cross-correlation Ray geometry – rotation Do not correct absolute position From cross-correlation centroid location Got et al., 1994 Waldhauser & Ellsworth, 2000 See Tutorial this afternoon for Methods

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Lengliné & Marsan, 2008 Size = Assumed stress drop + circular crack + moment – magnitude relation

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Bourouis & Bernard, 2007 Chen et al., 2008 Soultz-sous-Forêts Taiwan Radius estimated from corner frequency

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Murray & Langbein, 2006 Rau et al., 2007 Clusters of co-located, similar waveforms earthquakes, appears at the transition between fully locked and fully creeping areas

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Waldhauser & Schaff, 2008 Example from Northern-California Parkfield Is it related to fault slip velocity ?

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Rubin et al., 1999 San Andreas Fault Streaks of microearthquakes – along slip direction Rheological / frictional / geological / geometrical transition ?

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Observations - Timing

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YearNumber 18571 18812 19013 19224 19345 19666 20047 μ Δt = 24.5 yr σ Δt = 9.5 yr COV = 0.37 Time (years) Earthquake number Parkfield

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Repeaters off Kamaishi Repeating interval = 5.35 +/- 0.5 yrs Time (years)

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Waldhauser et al., 2004 Distance along strike (km) Year San-Andreas fault at Parkfield

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Waldhauser et al., 2004 Distance along strike (km) Year Periodic repeating ruptures

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Rubinstein et al., 2012 Quasi-periodic behavior of the slip activity

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Aseismic slip No interacting asperity The simplest model A locked seismic patch embedded in a fully creeping zone

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Slip on the creeping part Slip on the seismic asperity Time Slip

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Aseismic slip on the fault = seismic slip Time Slip d seis

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Aseismic slip on the fault = seismic slip Elastic solution for a circular crack

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Aseismic slip on the fault = seismic slip Elastic solution for a circular crack

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Aseismic slip on the fault = seismic slip Elastic solution for a circular crack Constant stress drop

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Chen et al., 2007

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1st Hypothesis The constant stress drop hypothesis is not correct Empirical fit to the data then suggests in order to have T r ~ M 0 1/6 Implies that the stress-drop is higher for small events. Stress levels reach 2 GPa for the smallest events (more than 10 times laboratory strength) This result is at odds with estimates based on seismic spectra Relation not consistent with established scaling relations for large earthquakes.

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Imanishi & Ellsworth, 2006

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Chen & Lapusta, 2009

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But not the estimated plate velocity – streaks close to locked section reduced velocity ?

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Slip on the creeping part Slip on the seismic asperity Time Slip Seismic slip

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Uchida, 2014 Off Kamaishi repeating sequence following Tohoku, 2011, Mw9 earthquake

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Lengliné & Marsan 2008 Schaff & Beroza, 1998

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Following Parkfield, 2004, Mw6 event

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Response of a velocity strengthening area to a stress-step Marone, 1991 The Omori like decay of RES is well rendered by the slip evolution of the creeping area following a stress step

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Nadeau & McEvilly, 1999

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Bourouis & Bernard, 2007

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Bouchon et al., 2011

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Kato & Nakagawa, 2014 Kato et al., 2012

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Repeating earthquake are local (sparse) creep-meter at depth Difficult to quantify if the seismic slip reflects the surrounding aseismic loading

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Time after 01/01/1984 (years) Number of earthquakes Complications to the idealized picture Repeating sequence of small micro-earthquakes at Parkfield

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Time after 01/01/1984 (years) Number of earthquakes Complications to the idealized picture Repeating sequence of small micro-earthquakes at Parkfield

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Interactions from nearby small events Chen et al., 2013 More isolated events = more periodic

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Vidale et al., 1994 How can strength of the interface build up so quickly between 2 events ? Healing of the interface

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What is an asperity ? (geometrical/frictional/geological …) What is the lifetime of an asperity ? In which case do we observe periodicity ? (density of asperity) Are repeating LFE earthquakes obeying a similar mechanism ? Questions

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2 examples of use of repeating earthquake sequences -Earthquake detection and time activity (with P. Ampuero) -Variation of source properties (with L. Lamourette, L. Vivin, N. Cuenot, J. Schmittbuhl)

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Parkfield

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Landweber deconvolution Example for one pair at one station

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Landweber deconvolution All pairs at all stations

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Sparse deconvolution 54 new detected events in the first 20s following a repeating earthquakes

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Stack aftershock sequence Typical rupture duration

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Wang et al., 2014

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Omori’s law extended almost up to the rupture duration Implies a very low c-value and thus a very large stress changes in the R&S Dieterich framework Seismicity rate Time (t/t a ) No flatenning of the earthquake rate at early times Is this particular to the repeating earthquakes ?

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Station surface sites 150 Hz sampling frequency 2010 11 months long circulation test 411 earthquakes recorded Largest magnitude event M2.3

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4 groups of similar events Relocation suggest a similar location Each group have at least one event larger than 1.4 4/6 of the largest events of the circulation are included in these groups

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SVD analysis (Rubinstein & Ellsworth, 2010 ) Up to a factor x 300 of moment ratio

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SVD analysis (Rubinstein & Ellsworth, 2010 ) Up to a factor x 300 of moment ratio

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For the largest event of each group

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Corner frequency of the largest event of each group f c ~ [10-20] Hz

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Wiener filter (equivalent to spectral ratio) Same rupture area

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The difference of seismic moment reflects a difference of seismic slip/ stress drop Increase of pore pressure lowers the normal stress on the fault plane 2 effects: Shear failure promoted (reach the Coulomb enveloppe) Stabilizes the slip Several instances of aseismic movements have been suggested in the Soultz reservoir We are observing a transition from unstable to stable slip on the interface Bourouis & Bernard, 2007

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Thank you

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