1. Jhungli-Taiwan 2009 Testing earthquake triggered landslides against earthquake aftershocks for space distributions (implications for triggering processes) l. Tatard, JR Grasso, S Garambois, A Helmstetter LGIT, Observatoire de Grenoble, France

2. Tools - Cross analysis of space distribution of aftershocks and landslides; stack-averaged patterns (statistical physics) Data: 5 sequences: Mw=7.6,7.6,7.2,6.6,5.4 (Thrusts + 1 normal faulting) Results : landslide = aftershock = > near field: aftershock static stress changes: how to go beyond correlation? = > landsliding: the ultimate site effect (need to work with the seismologist community) => landslide/aftershock: generic britlle crustal response to shocks (what we observe characterizes the medium) Testing earthquake triggered landslide against earthquake aftershocks for space distributions Objectives - Constrains on processes that possibly drive slope failures - Displacement (near-field, coseismic change in slope angle)? - Static – dynamic stress changes? - Strain (PGV), strain rates (PGA)? Jhungli-Taiwan 2009

3. Landslides and earthquake catalogues NZ, M=7.2, 2 003 NZ, Mw=5.4, 2004 x,y,ztimesizecompleteness aftershocks1-10 km<secM, MoMc landslidesfew km>day-weekm 2 - m 3 Vc ? NZ, 2001,2004 data from GNS >15% of data NZ, Mw=7.2, 2003

4. Landslides and earthquake catalogues NZ, M=7.2, 2003. NZ, Mw=7.2 Near field : ? (offshore) Middle field : N lds l > N aft Far field : N ldsl > ? N aft r -2 r -3 Gomberg and Fehlzer 2008

5. Landslides and earthquake catalogues NZ, M=7.2, 2 003 NZ, Mw=5.4, 2004 Numerous sources of possible bias (location, time, size) r -2 r -3 Near field : ? (offshore) Middle field : N lds l > N aft Far field : N ldsl > ? N aft Near field : Middle field : N lds l = N aft Far field : N ldsl = N aft r -1 Better fit between afts/landslide ….. when using the weakest dataset 2004

6. Landslides and earthquake catalogues NZ, M=7.2, 2003 California, Mw=6.6, 1994 Near field : N ldsl = N aft Middle field : N ldsl > N aft Far field : N ldsl > ? N aft

7. Landslides and earthquake catalogues NZ, M=7.2, 2003 Kashmir, Mw=7.6, 2005, 2004 Sato et al 2006

8. 4 m Kashmir, Mw=7.6, 2005, 2004 Pathier and Wright 2006 Grasso et al. 2006

9. Muzzaffarabad area

10. Kashmir, Mw=7.6, 2005 Surace fault trace and/or slide: peeling effect induce by change in slope value?

11. Landslides and earthquake catalogues NZ, M=7.2, 2003 Kashmir, Mw=7.6, 2005, 2004 Near field : N ldsl = N aft Middle field : N ldsl < N aft Far field : N ldsl < N aft

12. Landslides and earthquake catalogues NZ, M=7.2, 2003 Taiwan, Mw=7.6, 1999 Near field : N ldsl = N aft Middle field : N ldsl =/> N aft Far field : N ldsl = N aft

13. Landslides and earthquake catalogues NZ, Mw=5.4 5.6, 2004 Near field : N ldsl = N aft Middle field : N ldsl =/> N aft Far field : (Rotoehu aera: 223-312 mm rain within 3 days before the Mw5.6 event)

14. 5 case-studies - Landslide distribution in space mimics the one of aftershocks. - At a given distance Nldsl > Nafts (local data) Eqs triggerMwStyleDist Nslide/ Dist Nafts Eqs data NZ7.2T-(SF)>local Pakistan7.6T-SF<usgs Chi-chi7.6T-SF=usgs Northridge 6.6T>local NZ 5.4 N>local

15. Aftershock-Landslide response to quakes NZ, M=7.2, 2003NZ, Mw=5.4, 2004 Surface rupturerainrain (?)

16. Earthquake Triggered Landslides: Which candidates for driving processes? NZ, M=7.2, 2003 Ground motion: surface rupture << burried fault But how does it scale with distance (r) and earthquake size M=ln(L) ? PGA r -2 x L -1.4 PGV r -1.8 x L -1.6 Displ. r -1.5 x L -1.8 Neqs r -2 x L -2 Gomberg and Fehlzer, 2008 Pitarka et al. 2009

17. Earthquake Triggered Landslides: Which candidates for driving processes? NZ, M=7.2, 2003 PGA r -2 x L -1.4 PGV r -1.8 x L -1.6 Displ. r -1.5 x L -1.8 Neqs r -2 x L -2 Suggested Brodsky and Fehlzer, 2006 Gomberg and Fehlzer, 2008

18. Earthquake Triggered Landslides: Which candidates for driving processes? NZ, M=7.2, 2003 Earthquakes triggered slides: Saturation: 1-10 fault length Sharp decrease: >20 D/L

19. Earthquake Triggered Landslides: Which candidates for driving processes? PGA,PGV, Nldsl, Neqs : Northridge PGV, PGA, Nldsl, Neqs : Chi-Chi PGV-PGA Data from PEER web site PGA, PGV # f(f Hz, distance) Note: Meunier et al. GRL 07 use (distance to epicenter + %(surface))

20. Wave trapping Topographic & Landslide effects Amplification frequency : f 0 =V S /4H Frequency sensitivity : site effects Exemple of the Utiku landslide (NZ) collaboration LGIT (France) & GNS (NZ)

21. Frequency sensitivity of site effects (Utiku landslide, NZ) Spectral ratio On landslide On bedrock ■ Utiku, UL1 site, H1=49 m, V S =400 m/s, f o =2.2 Hz =V S /4H) ■ PGA(f hz ) observations differ from PGV (f hz ) observations particularly in the [0.3-5 ] Hz frequency range where landslides are sensitive.

22. Earthquake Triggered Landslides: Which candidates for driving processes? NZ, M=7.2, 2003 Landslide: - « simple » average pattern - f(distance)=aftershock - Tests for robustness (on going) Processes: - Aftershocks: D/L=1-3, static stress; D/L>10 ? Candidates for landslides ? - Is it definitively PGA for landslides? - PGA-PGV # f(f Hz, distance) => PGA implies D>>, V>> ? - Static-dynamics ? or -Generic crustal response to shock: not driven by PGA-PGV-Disp-…

23. Huge landslide in the near field: Constructive wave interferences in near field condition?

24. Meunier et al. GRL 07 warning:warning PGA threshold values for triggering are derived from valley seismic stations (lack of instrumented slope)