SCEC Award Number 11183 View PDF
Proposal Category Individual Proposal (Data Gathering and Products)
Proposal Title Rupture Characteristics and Segmentation of the 1892 Laguna Salada Fault Rupture: Setting the Stage for the 2010 El Mayor-Cucapah Earthquake
Investigator(s)
Name Organization
Karl Mueller University of Colorado, Boulder
Other Participants Following are collaborators: John Fletcher, Tom Rockwell, Andy Freed, Jian Lin.
SCEC Priorities A1, A3, A9 SCEC Groups Geology, USR
Report Due Date 02/29/2012 Date Report Submitted N/A
Project Abstract
 Objectives of this project were to map and measure surface displacement in the Mw 7.2 1892 Laguna Salada earthquake and to compare the strain field with the Mw 7.2 2010 El Mayor-Cucapah earthquake. Results of the mapping suggest the earthquake in 1892 ruptured a segmented set of faults, separated by seismic gaps. Whereas components of extensional and dextral slip and their proportion in comparison to fault strike in 1892 were generally similar along segments, distinct differences existed between segments. The similar magnitude of 1892 and 2010 are a product both the difference in rupture length and cumulative slip for the two earthquakes. Toggling of slip is apparent for two of the 5 main 1892 segments; one pair (2010 La Puerta and 1892 southern Laguna Salada) correlates almost exactly (i.e. segment endpoints) in spite of dramatic kinematic complexity along the Laguna Salada fault. Implications of our work suggest that seismic moment release during large earthquakes in the Salton Trough – Northern Gulf of California region is anything but simple. Two parallel fault zones, lying either athwart or less than 4 kilometers apart release strain at dramatically different timescales, with average recurrence, displacement and fault length varying by a factor of 2 during the Holocene. In addition, fault segmentation is also complex, characterized by extensional stepovers that reflect an evolving 1-2 km wide shear zone. In some instances fault segments that ruptured in 1892 were reoccupied in 2010, further exemplifying complexity in moment release at millennial timescales.
Intellectual Merit This research has contributed to a better understanding of time-space patterns of seismic moment release in complex transtensional fault zones. Further it illustrates how detailed field measurements of displacement and segmentation of fault zones while illuminating fundamental differences in large magnitude earthquakes and the utility of post event lidar data for earthquake geology.
Broader Impacts As part of the SCEC3 summer intern program, a University of Colorado geology undergrad, Patrick Patton worked with Mueller to compile field measurements, develop geometric model of the fault systems that ruptured in 1892 and 2010 and presented a poster at the annual meeting. Patrick felt the internship was a highlight of his undergraduate career and provided valuable experience that will help propel him into a Masters degree (he has subsequently applied for admission into the University of Washington and CU-Boulder graduate programs in geology).
Exemplary Figure Figure 3 Detailed fault map of the Laguna Salada fault zone derived from lidar topography. The lower panel illustrates the complexity of the relatively young array of faults that are becoming linked across a series of releasing bends. One zone of diffuse extension apparently did not break in 1892 (i.e. that linked longer strands with a larger component of dextral slip). Note the location of the (white) fault strand that formerly accommodated most of the shear in the southern portion of the LSFZ.