Auxiliary Material for Paper 2011GL050828

Farallon slab detachment and deformation of the Magdalena Shelf, southern Baja 
California

Daniel Brothers 
Woods Hole Coastal and Marine Science Center, U.S. Geological Survey, 
Woods Hole, Massachusetts, USA

Scripps Institution of Oceanography, University of California, San Diego, 
La Jolla, California, USA

Alistair Harding
Scripps Institution of Oceanography, University of California, San Diego, 
La Jolla, California, USA

Antonio Gonzalez-Fernandez
Department of Geology, CICESE, 
Ensenada, Mexico

W. Steven Holbrook 
Department of Geology and Geophysics, University of Wyoming, 
Laramie, Wyoming, USA

Graham Kent 
Nevada Seismological Laboratory, University of Nevada, Reno, 
Reno, Nevada, USA

Neal Driscoll 
Scripps Institution of Oceanography, University of California, San Diego, 
La Jolla, California, USA

John Fletcher
Department of Geology, CICESE, 
Ensenada, Mexico

Dan Lizarralde,6 
Woods Hole Oceanographic Institution, 
Woods Hole, Massachusetts, USA

Paul Umhoefer 
School of Earth Sciences and Environmental Sustainability, 
Northern Arizona University, 
Flagstaff, Arizona, USA

Gary Axen
Department of Earth and Environmental Science, 
New Mexico Institute of Mining and Technology, 
Socorro, New Mexico, USA


Brothers, D., A. Harding, A. Gonzalez-Fernandez, W. S. Holbrook, G. Kent, 
N. Driscoll, J. Fletcher, D. Lizarralde, P. Umhoefer, and G. Axen (2012), 
Farallon slab detachment and deformation of the Magdalena Shelf, southern 
Baja California, Geophys. Res. Lett., 39, L09307, doi:10.1029/2011GL050828.

Introduction

This auxiliary material contains eight figures.

1. 2011gl050828-fs01.pdf
Figure S1. Line 0 uninterpreted multichannel seismic profile.

2. 2011gl050828-fs02.pdf
Figure S2. Correlation between Line 0 seismic horizons and DSDP Site 471 
[Yeats et al., 1981].

3. 2011gl050828-fs03.pdf
Figure S3. Example record sections for OBS receivers 1 and 3 on the 
Magdalena Shelf. Solid lines are arrival picks and dashed lines are 
predicted arrivals based on raytracing through the fi nal velocity model. 
Magenta lines are Pg (crustal) arrivals, green are Pn (mantle) arrivals 
and blue lines are reflections off the moho. Pa picks (yellow) on OBS 3 
represent refractions through the older compacted sediments of the 
syncline feature seen in Figure 3. PmP picks were not used in the 
inversion due to inconsistencies in data quality between receivers, but 
will be added in the future. Data quality for Pg arrivals is generally 
good for shot-receiver offsets of 50 km and less and 70 km and less for 
Pn arrivals.

4. 2011gl051828-fs04.pdf
Figure S4. Example record sections for land receivers 4 (western shots) 
and 1 (eastern shots). Land 04 recorded excellent data for shots up to 
120 km away from the receiver.

5. 2011gl050828-fs05.pdf
Figure S5. Example record sections for OBS receivers 6 and 11 in the Gulf 
of California. The most prominent feature in the data is the basin 
surrounding the Pescadero Transform Fault.

6. 2011gl050828-fs06.pdf
Figure S6. Derivative weight sum (DWS) plot (B) of the final model (A) to 
demonstrate ray coverage. White regions are unconstrained by the 
raypaths. To first order, the velocity information of a particular 
diving-wave travel time pick is concentrated toward the bottoming point 
of its associated ray, however, derivative weight sum (DWS) data is a 
useful measure of ray density in the neighborhood of model nodes [Toomey 
and Foulger, 1989]. DWS for a node is similar to the ray hit count, but 
weighted by the ray-node separation and raypath length in the vicinity of 
the node. The final model includes four layer boundaries and is 
parameterized using a 0.1 km vertical spacing and 0.5 km horizontal 
spacing. MCS data were used to constrain the geometry of sedimentary 
basins and wide-angle travel times were used to model basins that were 
not fully imaged in MCS profiles.

7. 2011gl050828-fs07.pdf
Figure S7. Picked (dashed lines) and predicted (solid lines) travel time 
curves. The model produced good agreement between picks and predictions. 
The ?2 data misfit for the final model was 2.5.

8. 2011gl050828-fs08.pdf
Figure S8. (A) Simulated raypaths for rays reflected off the high 
velocity zone inferred to be relic Farallon slab. (B) Predicted arrivals 
for slab-bounces overlain on the record section for OBS 3. Magenta lines 
are Pg (crustal) arrivals, green are Pn (mantle) arrivals and blue lines 
are PmP reflections off the moho. Maroon and tourqouise lines are the 
uncertainty bounds for slab reflections. We do no observe evidence that 
the slab extends deeper than the root of the Baja California microplate.