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SSIP John Hole, Virginia Tech Joann Stock, Caltech Gary Fuis, USGS Menlo Park Antonio Gonzalez-Fernandez, CICESE Octavio Lazaro-Mancilla, UABC
SSIP: Salton Seismic Imaging Project A Joint GeoPRISMS + EarthScope + USGS Investigation of
Rift Initiation and Evolution
Hole GeoPRISMS-EarthScope ENAM Workshop 2011
Wet-SSIP Neal Driscoll, Scripps Graham Kent, U. Nevada Reno Alistair Harding, Scripps Broadband-SSIP Simon Klemperer, Stanford
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Hole GeoPRISMS-EarthScope ENAM Workshop 2011
Salton Trough
Colorado River
same amount of extension along entire length of Gulf
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Transitional Crust at Rifted Continental Margins
magma dominated
“other”
stretching dominated
Hole GeoPRISMS-EarthScope ENAM Workshop 2011
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Lithosphere in Imperial Valley
sediment
metamorphosed sediment
gabbro
hot upper mantle
magmatism from mantle
sedimentation from Colorado River
3-6 km
20-24 km
12-16 km
MOHO
entirely new crust, <6 Myr old 0 km
Hole GeoPRISMS-EarthScope ENAM Workshop 2011
future continental margin
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Sedimentation & Magmatism
from Schmitt & Vazquez, 2006
thick sediment affects magmatism, heat flow magmatism affects sediment (metamorphism) role of hydrothermal circulation together create brand-new crystalline crust
Hole GeoPRISMS-EarthScope ENAM Workshop 2011
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Oblique Rifting
Brawley Seismic Zone
strain partitioning rift transform brittle ductile magmatic
from Shearer et al. 2005 Hole GeoPRISMS-EarthScope ENAM Workshop 2011
SAF
IF
Salton Buttes
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SSIP Goals
rift initiation and evolution roles of and interactions between: - continental stretching (brittle & ductile) - magmatism - sedimentation partitioning of strain during continental breakup
Hole GeoPRISMS-EarthScope ENAM Workshop 2011
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Earthquake Hazards
San Andreas Fault + at least 4 faults in Imperial & Mexicali Valleys with historic magnitude 6-7 earthquakes
Hole GeoPRISMS-EarthScope ENAM Workshop 2011
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Fault Dip
earthquakes not under San Andreas Fault trace
from Shearer et al. 2005
Hole GeoPRISMS-EarthScope ENAM Workshop 2011
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SSIP Goals
rift initiation and evolution roles of and interactions between: - continental stretching (brittle & ductile) - magmatism - sedimentation partitioning of strain during continental breakup earthquake hazards parameters for fault-earthquake models and for strong ground motion simulation - subsurface geometry of faults - geometry & velocity of sedimentary basins - regional 3D velocity model
Hole GeoPRISMS-EarthScope ENAM Workshop 2011
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SSIP
SSIP onshore seismic refraction & reflection Wet-SSIP marine seismic refraction & reflection Broadband-SSIP onshore broadband teleseismic
Hole GeoPRISMS-EarthScope ENAM Workshop 2011
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SSIP
SSIP onshore seismic refraction & reflection Wet-SSIP marine seismic refraction & reflection Broadband-SSIP onshore broadband teleseismic
Marine Geology & Geophysics
Geophysics
Hole GeoPRISMS-EarthScope ENAM Workshop 2011
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January 2011 – June 2012 42 broadband seismic 16 personnel, 5 universities
Broadband-SSIP
Hole GeoPRISMS-EarthScope ENAM Workshop 2011
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March 2011 explosive shots 126 shots total 33,329 kg median 115 kg
SSIP
Hole GeoPRISMS-EarthScope ENAM Workshop 2011
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March 2011 airgun shots 2330 shots ~100 m spacing
Wet-SSIP
Hole GeoPRISMS-EarthScope ENAM Workshop 2011
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March 2011 (<3 weeks) seismometers: 3958 1-component Texan sites 277 3-component RT130 sites 78 3-component OBS sites
SSIP+Wet-SSIP
Hole GeoPRISMS-EarthScope ENAM Workshop 2011
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March 2011 (<3 weeks) ~120 personnel > 50 students 31 colleges/universities
SSIP+Wet-SSIP
Hole GeoPRISMS-EarthScope ENAM Workshop 2011
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Imperial Valley Shot Gather
shot shot-receiver distance (km)
60 40 20
3
6
9
12
15
time
(s)
0
Mexico USA
basin reverb.
reflection from lower crust
~5.5 km/s Pg
~2 km/s sed. N S
Hole GeoPRISMS-EarthScope ENAM Workshop 2011
confirms crustal layers, but at order of magnitude better sampling
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Shot Gather Across Salton Trough
shot Tijuana
Imperial Fault
Colorado River
reflection from Moho
reflection from Moho
Hole GeoPRISMS-EarthScope ENAM Workshop 2011
redu
ced
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Velocity Model: Along Imperial Valley
Han & Hole
slow “basement” = metamorphosed sediment
SE NW
Hole GeoPRISMS-EarthScope ENAM Workshop 2011
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Velocity Model: Along S. Shore of Salton Sea
Delph & Hole
slow “basement” = metamorphosed sediment much shallower under geothermal & volcanic field
Sand Hill Fault SW NE
Hole GeoPRISMS-EarthScope ENAM Workshop 2011
IRIS undergrad intern
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Reflection Image: Along Salton Sea
Driscoll, Kent, Harding, Kell, & Babcock
VE ~12:1
normal faults in sediments rapid subsidence in south
Hole GeoPRISMS-EarthScope ENAM Workshop 2011
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SSIP has barely begun analysis
rift processes earthquake hazards
Hole GeoPRISMS-EarthScope ENAM Workshop 2011 http://www.geophys.geos.vt.edu/hole/salton/