Report

Repeating Earthquakes Olivier Lengliné - IPGS Strasbourg Cargese school Please interrupt Questions / remarks 1 – Review of Repeating earthquake observations & interpretations 2 – Two examples of application Observations - Waveforms Nadeau & Johnson, 1998 Parkfield, California – Mw6.0 USGS De Bilt, The Netherlands Bakun et al., 2005 Off Kamaishi, Japan – M4.9 Uchida et al., 2012 Time (s) Chihshang fault, Taiwan Chen et al., 2008 Soultz-Sous-Forêts geothermal reservoir, France 9 events 9 events 13 events BRGM 19 events 0.0 0.5 1.0 1.5 2.0 Time (s) 2.5 3.0 3.5 San-Andreas Fault Rubinstein et al., 2012 Schaff & Beroza, 1998 u(t) = Source * Path * Station u(t) = Source * Path * Station u(t) = Source * Path * Station Station is the same Change in medium property, [e.g Poupinet et al., 1984] Change in source properties, [e.g. Lengliné & Got, 2011] Lengliné and Got, 2011 Directivity Velocity variations Poupinet et al., 1984 u(t) = Source * Path * Station ! Homogeneous medium waveform similarity Station the same Change in medium property, [e.g Poupinet et al., 1984] Change in source properties, [e.g. Lengliné & Got, 2011] Observations - Locations Waldhauser et al., 2004 Parkfield Murray & Langbein, 2006 Off Kamaishi Moment release distribution Relative moment released normalized by each maximum value Okada et al., 2002 Earthquake relative relocation Uncertainties P-wave picks Uncertainties of the velocity model 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 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 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 Lengliné & Marsan, 2008 Size = Assumed stress drop + circular crack + moment – magnitude relation Taiwan Soultz-sous-Forêts Bourouis & Bernard, 2007 Chen et al., 2008 Radius estimated from corner frequency Murray & Langbein, 2006 Clusters of co-located, similar waveforms earthquakes, appears at the transition between fully locked and fully creeping areas Rau et al., 2007 Example from Northern-California Parkfield Waldhauser & Schaff, 2008 Is it related to fault slip velocity ? San Andreas Fault Rubin et al., 1999 Streaks of microearthquakes – along slip direction Rheological / frictional / geological / geometrical transition ? Observations - Timing Parkfield 8 Earthquake number 7 6 5 4 3 2 Year Number 1857 1 1 1881 2 1901 3 0 1800 1922 4 1934 5 1966 6 2004 7 1850 μΔt = 24.5 yr σΔt = 9.5 yr COV = 0.37 1900 1950 Time (years) 2000 2050 Repeaters off Kamaishi Repeating interval = 5.35 +/- 0.5 yrs Time (years) Year San-Andreas fault at Parkfield Distance along strike (km) Waldhauser et al., 2004 Year Periodic repeating ruptures Distance along strike (km) Waldhauser et al., 2004 Rubinstein et al., 2012 Quasi-periodic behavior of the slip activity The simplest model No interacting asperity A locked seismic patch embedded in a fully creeping zone Aseismic slip Slip on the creeping part Slip Slip on the seismic asperity Time dseis Slip Aseismic slip on the fault = seismic slip Time Aseismic slip on the fault = seismic slip Elastic solution for a circular crack Aseismic slip on the fault = seismic slip Elastic solution for a circular crack Aseismic slip on the fault = seismic slip Elastic solution for a circular crack Constant stress drop Chen et al., 2007 1st Hypothesis The constant stress drop hypothesis is not correct Empirical fit to the data then suggests in order to have Tr ~ M01/6 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. Imanishi & Ellsworth, 2006 Chen & Lapusta, 2009 Chen & Lapusta, 2009 But not the estimated plate velocity – streaks close to locked section reduced velocity ? Slip on the creeping part Slip Slip on the seismic asperity Time Seismic slip Off Kamaishi repeating sequence following Tohoku, 2011, Mw9 earthquake Uchida, 2014 Lengliné & Marsan 2008 Schaff & Beroza, 1998 30 25 Number of earthquakes 20 15 10 5 0 1985 1990 1995 Following Parkfield, 2004, Mw6 event 2000 Time( years) 2005 2010 2015 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 Nadeau & McEvilly, 1999 Nadeau & McEvilly, 1999 Bourouis & Bernard, 2007 29˚00' 41˚00' 29˚30' 30˚00' 30˚30' 31˚00' 41˚00' UCG 40˚30' 29˚00' 29˚30' 30˚00' 30˚30' Bouchon et al., 2011 40˚30' 31˚00' Kato & Nakagawa, 2014 Kato et al., 2012 Repeating earthquake are local (sparse) creep-meter at depth Difficult to quantify if the seismic slip reflects the surrounding aseismic loading Complications to the idealized picture 8 Number of earthquakes 7 6 5 4 3 2 1 0 0 5 10 15 Time after 01/01/1984 (years) Repeating sequence of small micro-earthquakes at Parkfield 20 Complications to the idealized picture 8 Number of earthquakes 7 6 5 4 3 2 1 0 0 5 10 15 Time after 01/01/1984 (years) Repeating sequence of small micro-earthquakes at Parkfield 20 Interactions from nearby small events More isolated events = more periodic Chen et al., 2013 Chen et al., 2013 How can strength of the interface build up so quickly between 2 events ? Healing of the interface Vidale et al., 1994 Questions 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 ? 2 examples of use of repeating earthquake sequences - Earthquake detection and time activity (with P. Ampuero) - Variation of source properties Cuenot, J. Schmittbuhl) (with L. Lamourette, L. Vivin, N. Parkfield Landweber deconvolution Example for one pair at one station Landweber deconvolution All pairs at all stations Sparse deconvolution 54 new detected events in the first 20s following a repeating earthquakes Typical rupture duration Stack aftershock sequence Wang et al., 2014 Omori’s law extended almost up to the rupture duration No flatenning of the earthquake rate at early times Is this particular to the repeating earthquakes ? Seismicity rate Implies a very low c-value and thus a very large stress changes in the R&S Dieterich framework Time (t/ta) 2010 11 months long circulation test 411 earthquakes recorded Largest magnitude event M2.3 Station surface sites 150 Hz sampling frequency • • • • 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 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 SVD analysis (Rubinstein & Ellsworth, 2010 ) Up to a factor x 300 of moment ratio SVD analysis (Rubinstein & Ellsworth, 2010 ) Up to a factor x 300 of moment ratio For the largest event of each group 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 0.0 0.5 1.0 1.5 2.0 2.5 Corner frequency of the largest event of each group fc ~ [10-20] Hz 3.0 3.5 Wiener filter (equivalent to spectral ratio) Same rupture area 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 Bourouis & Bernard, 2007 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 Thank you