Quick fault-plane identification by a
geometrical method: The Mw6.2
Leonidio earthquake, 6 January
2008, Greece and some other recent
applications
J. Zahradnik, F. Gallovic
Charles University in Prague
E. Sokos, A. Serpetsidaki, G-A. Tselentis
University of Patras
Why we need to know
the fault plane ?
• Shake maps
• Aftershock prediction
• Stress field
Why we need to know
the fault plane quickly?
• Shake maps
• Aftershock prediction
Which nodal plane is the fault
plane ?
• Aftershock distribution
• Finite-extent source models; waveform
modeling
• Geometrical configuration of hypocenter
(H) and centroid (C)
Which nodal plane is the fault
plane ?
• Aftershock distribution … too slow
• Finite-extent source models; waveform
modeling
• Geometrical configuration of hypocenter
(H) and centroid (C)
Which nodal plane is the fault
plane ?
• Aftershock distribution … too slow
• Finite-extent source models; waveform
modeling … too slow
• Geometrical configuration of hypocenter
(H) and centroid (C)
Which nodal plane is the fault
plane ?
• Aftershock distribution … too slow
• Finite-extent source models; waveform
modeling … too slow
• Geometrical configuration of hypocenter
(H) and centroid (C) … quick enough !
H-C method
H and C are in the same plane (I or II) of the conjugated
fault-plane solutions. H-C distance must be larger enough; M>6.
Multiple H and C solutions (uncertainty) help
to prefer one of the two planes.
H-C method applied to five M>6 events in 2008
H-C method applied to five M>6 events in 2008
This presentation: 2 examples
M 6.2 Leonidio, Jan 6, 2008
depth 60-80 km
Waveform
modeling
for CMT
10 near-regional
BB stations
f < 0.07 Hz
CENTROID
HYPOCENTER
„Collective“ solutions =
including uncertainties of H and CMT
H
H
red, green: nodal planes of three CMT solutions
The weakly dipping nodal plane
identified as the fault plane
Strike 213°
Dip
34°
Rake 5°
The ‘green’ nodal plane is
the fault plane
because it encompasses
the (uncertain) hypocenter.
Practical output:
Report to EMSC within 1 week
after the earthquake
report_jan06.pdf
(in Earthquake News & Highlights)
Consistence with the
regional stress field
(Kiratzi
& Papazachos, 1995)
T of this earthquake
T of regional field
Validation without
aftershocks ?
sub-horizontal
slip vector
Slip vector and
regional stress field
allow us to resolve the
traction and evaluate the
Coulomb Failure Function.
TVN
negative
TVN
positive
The
Coulomb Failure Function
supports
the sub-horizontal slip.
TVS: tangential traction parallel to slip
TVN: normal traction
CFF=TVS+mTVN
CFF larger for plane II
because TVN is positive
Nodal
plane
TVS
TVN CFF
I
0.794
-0.192
0.696
II
0.790
0.552
1.066
Example 2
Mw 6.3 Andravida June 8, 2008
depth ~ 20 km
Strike 210°
Dip
85°
Rake 179°
Mw 6.3 Andravida June 8, 2008
depth ~ 20 km
X-Y-Z
X-Y-Z
10
10
0
0
-10
Depth
5
Depth
5
-50
0
-20
0
-10
-5
-30
-15
-5
-10
-5
0
North-South (km)
5
10
15
-5
0
North-South (km)
5
-10
10
East-West (km)
East-West (km)
H: UPSL and THE
C: Harvard
H: UPSL
C: Mednet
Strike 210, a right-lateral strike slip fault
-10
Report to EMSC 7 hours after the
earthquake
report_june08.pdf
Abundant aftershocks (24-hours,
NOA) validate the quick faultplane guess (7 hours)
Strong-motion accelerograms
(NOA) reveal a different duration:
Amaliada
dist. ~25 km
Patras
dist, ~35 km
Does a simple finite-extent
source model based on the H-C
result explain the data?
Patras
Amaliada
C
SW
H
NE
Typical finite-source synthetics
reproduce
Amaliada
the duration
110
and
support
synth. acceleration (cm/s2)
H-C results
Patras
80
0
10
20
time (sec)
Amaliada: backward
Patras: forward
30
Further support: azimuthal
variation of the differential travel
time t’-t
t … hypocentre
t‘ … asperity first brake
(After Takenaka et al., 2005)
Differential travel time (sec)
1
EVR
0.8
UPR
LTK
VLS
MAM
RLS
EFP
0.6
ITM
GUR
VLX
PYL
0.4
ZAK
VAR
0.2
0
0
100
200
Azimuth (deg)
300
400
Conclusion
• H-C method is a simple tool for quick
identification of the fault plane
• Applicable with ‘manual’ locations and
CMT agency solutions (within a few hours)
• Collective solutions account for uncertainty
through scatter in the H and C solutions
• So far the best validated: June 8, 2008
Andravida (=> rupture propagation to NE)
Full paper and e-supplement:
Seism. Res. Letters, 79, 653-662, 2008
Try also a 3D ‘animation’ tool (hcplot.m).
H-C geometrical
method applied
to five M>6 events
in 2008
===========================================
Event
Fault plane
less likely
Report
strike dip rake
to EMSC
===========================================
Leonidio Jan 6
213 34 5 119 87 124
1 week
Methoni Feb 14 311 14 95 126 76 89
1 day
Methoni Feb 20 153 78 153 249 64 13
1 day
Andravida Jun 8 210 85 179 300 89 5
7 hours
Rhodos Jul 15 262 90 -38 352 52 -180 14 days