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Seismicity and Faulting in the Southern Gulf of California
Danielle F. Sumy (Lamont-Doherty Earth Observatory), James B. Gaherty (Lamont-Doherty Earth Observatory), Tobias
Diehl (Lamont-Doherty Earth Observatory), Won-Young Kim (Lamont-Doherty Earth Observatory), John Collins (Woods-
Hole Oceanographic Institution)
The Sea of Cortez Ocean-Bottom Array (SCOOBA) seismic experiment consists of a 4-component broadband ocean-bottom
seismic (OBS) array that recorded earthquakes and other natural seismic signals for nearly 12 months between October
2005 and October 2006. The 14-station array was designed to complement the onshore NARS-Baja experiment run by Utrecht
University, Cal Tech, and CICESE. Two subarrays were centered within the Alarcon and Guaymas basins, coinciding with previous
refraction and MCS lines [Lizarralde et al., 2007], with ~20 km spacing. Four additional instruments were deployed at ~100
km spacing. Over 650 earthquakes (depths < 35 km) were recorded by the array, with ~320 M>3.5 earthquakes and seven M>5
strike-slip events within the southern gulf that are accompanied by several foreshocks and aftershocks. Most of these events are
located on the major NW-SE strike slip faults that delineate the plate boundary, but a few appear to be located on faults well
away from the nominal plate boundary. For sufficiently well-recorded and paired events, we are in the process of applying the
hypoDD double-difference algorithm to obtain high-precision relative relocations. Additionally, we are working towards modeling
the Rayleigh waves of ~30 events to determine the mechanisms of on- and off-axis activity. These locations and mechanisms
of earthquake activity will improve our understanding of the distribution of seismic deformation within the greater extensional
zone in the southern GoC. These data have been archived at the IRIS DMC, and are openly available to the community.
References
Lizarralde, D., G. J. Axen, H. E. Brown, J. M. Fletcher, A. Gonzalez-Fernandez, A. J. Harding, W. S. Holbrook, G. M. Kent, P. Paramo, F.
Sutherland and P. J. Umhoefe, Variation in the styles of rifting in the Gulf of California, Nature, 448, 466-469, 2007.
Acknowledgements: Funding is from the NSF MARGINS program, award number OCE 0436411 for James Gaherty at LDEO, and OCE
0305140 for John Collins at WHOI.
Figure 1. Location of the SCOOBA OBS stations (triangles),
as well as complementary on-shore broadband
NARS-Baja stations (blue squares). Also shown
are Global CMT mechanisms for seven large events
recorded by the array, our modeled mechanism for the
27 November 2005 event, and the locations for ~300 of
our best-located events (black circles).
30º
28º
NE74
Mw 6.5
2006 Jan 4
Mw 5.2
NE81
Mexico
Mw 5.1
2006 May 28
Mw 5.2
NE75
N02
NE76
I01
2006 July 30
Mw 5.9
NE82
2005 Nov 27
Mw 5.0
26º
Baja California Sur
NE77
I02
2006 May 11
Mw 4.8
24º
SCOOBA Stations
Data Recovered
Disk Failure
x OBS lost
On-shore Stations
NARS-Baja
NE84
NE78 I04
NE85
S01x
NE79
S03
NE83
S06
22º
Events
Potential CMTs
Regional Locations
2006 Jan 5
Mw 5.0
I06
-114º -112º -110º -108º
II-50 | 2010 IRIS Core Programs Proposal | Volume II | Earthquake Source Studies