USGS • WHOI • DPRI Coulomb Stress Transfer Model
For the 12 Jan 2010 Mw=7.0 Haiti Earthquake
Version 2.0, 21 Jan 2010, 4:15PM PST
Jian Lin (jlin@whoi.edu), Ross Stein (rstein@usgs.gov), Volkan Sevilgen
(vsevilgen@usgs.gov), and Shinji Toda (toda@rcep.dpri.kyoto-u.ac.jp)
Interpretation of the results. The greatest area of concern for a large triggered shock is
immediately to the east of the 12 Jan 2010 rupture on section 1 of the Enriquillo fault,
where stress is calculated to have risen by about 2-4 bars, depending on location.
Typically, stress increases of this magnitude are associated with aftershocks, but thus far
none has struck on this section, which comes within 5 km of Port-au-Prince. The next
most likely site for a subsequent fault rupture lies to the west of the 12 Jan rupture along
section 2, where the stress is calculated to have brought about 1 bar closer to failure on
the Enriquillo fault west of a 5-km-wide ‘en echelon’ offset. No aftershocks have struck
on this section either. No thrust fault sustained an equivalent stress increase. The lower
15-20 km of thrust 9 sustained a calculated stress increase of 0.5 bars, but the upper
portions are inhibited from failure. Thrust faults 3, 4, 6, and 8 are calculated to have been
brought about 0.1 bar closer to failure, a relatively modest amount. In general, stress
increases of ≥1 bar are associated with increased rates of seismicity; stress changes of
less than 0.1 bars are generally not associated with observed seismicity increases.
Modeling parameters and assumptions. The source fault is the 19 January 2010
version of Gavin Hayes’ 180-patch unilateral rupture model, hai_ffm2.inp model, with a
seismic moment of 5.44 x 1026 dyne cm (Mw=7.09). Only an earlier version is currently
available on the NEIC website. The source model is on a single plane, and so simplifies
the likely rupture geometry. The surrounding faults are inferred from Figure 5 of Mann et
al. (Tectonics, 21, 1057, doi:10.1029/2001TC001304, 2002). In the absence of field data,
we have assumed the thrust faults extend to a depth of 20 km, dip 45°, and undergo pure
reverse slip. We assume the strike-slip faults extend to 24 km depth and dip 70° to the
north (as in the 12 Jan mainshock), and undergo pure strike-slip. We use a uniform elastic
halfspace with shear modulus of 3.2 x 1011 dyne cm-2, and a uniform fault friction of 0.4.
Lower friction might be appropriate on the strike-slip faults and higher friction on reverse
faults. Calculations were made using Coulomb 3.1.09, which can be freely downloaded
along with the user manual and tutorials from http://www.coulombstress.org.
Acknowledgements. We are grateful for Coulomb model calibration from Eric Calais
(Purdue University), the active fault mapping of Paul Mann (University of Texas Austin),
and essential source model guidance from Gavin Hayes (NEIC/USGS).
19.4°
Haiti
Legend
6
Un-named faults
5
Population density
(Landscan 2004)
D.R.
NEIC epicenter
19.0°
Gon
ave
18.6°
a
10
2
E n r iq u i l l o
18.2°
7
xtent
ftershock e
ture
12 Jan rup
1
4
fa u lt
Port-au-Prince
9
6
8
40 km
17.8°
3
USGS • WHOI • DPRI Coulomb Stress Model
For the 12 Jan 2010 Mw = 7.0 Haiti Earthquake
Version 2.0, 21 Jan 2010, 4:15PM PST
−73.4°
−0.5
−73.0°
−72.6°
−72.2°
−71.8°
0.0
Reduced
0.5 Coulomb stress changes (bars)
on individual ‘receiver’ faults
friction coeff. = 0.4
Hazard Increased
Jian Lin (jlin@whoi.edu), Ross Stein (rstein@usgs.gov), Volkan Sevilgen (vsevilgen@usgs.gov),
and Shinji Toda (toda@rcep.dpri.kyoto-u.ac.jp)