jhungli-taiwan 2009 testing earthquake triggered landslides against earthquake aftershocks for space...
Post on 29-Jan-2016
218 Views
Preview:
TRANSCRIPT
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
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
Landslides and earthquake catalogues
NZ, M=7.2, 2003
NZ, Mw=5.4, 2004 x,y,z time size completenes
s
aftershocks 1-10 km <sec M, Mo Mc
landslides few km >day-week m2- m3 Vc ?
NZ, 2001,2004 data from GNS>15% of data
NZ, Mw=7.2, 2003
Landslides and earthquake catalogues
NZ, M=7.2, 2003
.
NZ, Mw=7.2
Near field : ? (offshore)Middle field : Nldsl > Naft Far field : Nldsl > ? Naft
r-2
r-3
Gomberg and Fehlzer 2008
Landslides and earthquake catalogues
NZ, M=7.2, 2003
NZ, Mw=5.4, 2004
Numerous sources of possible bias (location, time, size)
r-2
r-3Near field : ? (offshore)Middle field : Nldsl > Naft Far field : Nldsl > ? Naft
Near field :Middle field : Nldsl = Naft Far field : Nldsl = Naft
r-1
Better fit between afts/landslide
….. when using the weakest dataset 2004
Landslides and earthquake catalogues
NZ, M=7.2, 2003California, Mw=6.6, 1994
Near field : Nldsl = Naft Middle field : Nldsl > Naft Far field : Nldsl > ? Naft
Landslides and earthquake catalogues
NZ, M=7.2, 2003Kashmir, Mw=7.6, 2005, 2004
Sato et al 2006
4 m
Kashmir, Mw=7.6, 2005, 2004 Pathier and Wright 2006
Grasso et al. 2006
Muzzaffarabad area
Kashmir, Mw=7.6, 2005
Surace fault trace and/or slide: peeling effect induce by change in slope value?
Landslides and earthquake catalogues
NZ, M=7.2, 2003Kashmir, Mw=7.6, 2005, 2004
Near field : Nldsl = Naft Middle field : Nldsl < Naft Far field : Nldsl < Naft
Landslides and earthquake catalogues
NZ, M=7.2, 2003Taiwan, Mw=7.6, 1999
Near field : Nldsl = Naft Middle field : Nldsl =/> Naft Far field : Nldsl = Naft
Landslides and earthquake catalogues
NZ, Mw=5.4 5.6, 2004
Near field : Nldsl = Naft Middle field : Nldsl =/> Naft Far field :
(Rotoehu aera: 223-312 mm rain within 3 days before the Mw5.6 event)
5 case-studies
- Landslide distribution in space mimics the one of aftershocks.- At a given distance Nldsl > Nafts (local data)
Eqs trigger
Mw Style Dist Nslide/
Dist Nafts
Eqs data
NZ 7.2 T-(SF) > local
Pakistan 7.6 T-SF < usgs
Chi-chi 7.6 T-SF = usgs
Northridge 6.6 T > local
NZ 5.4 N > local
Aftershock-Landslide response to quakes
NZ, M=7.2, 2003 NZ, Mw=5.4, 2004
Surface rupture rainrain (?)
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
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, 2006Gomberg and Fehlzer, 2008
Earthquake Triggered Landslides: Which candidates for driving processes?
NZ, M=7.2, 2003
Earthquakes triggered slides: Saturation: 1-10 fault lengthSharp decrease: >20 D/L
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(fHz, distance)
Note: Meunier et al. GRL 07 use (distance to epicenter + %(surface))
Wave trapping
Topographic& Landslide effects
Amplification frequency : f0=VS/4H
Frequency sensitivity : site effects
Exemple of the Utiku landslide (NZ)
collaboration LGIT (France) & GNS (NZ)
Frequency sensitivity of site effects(Utiku landslide, NZ)
Spectral ratio
On landslide
On bedrock
■ Utiku, UL1 site, H1=49 m, VS=400 m/s, fo=2.2 Hz =VS/4H)
■ PGA(fhz) observations differ from PGV (fhz) observationsparticularly in the [0.3-5 ] Hz frequency range where landslides are sensitive.
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(fHz, distance)=> PGA implies D>>, V>> ?
- Static-dynamics ?
or-Generic crustal response to shock: not driven by PGA-PGV-Disp-…
Huge landslide in the near field:
Meunier et al. GRL 07
warning:warningPGA threshold values for triggeringare derived from valley seismic stations(lack of instrumented slope)
top related