SCEC Award Number 15012 View PDF
Proposal Category Individual Proposal (Data Gathering and Products)
Proposal Title Renewal:Using Borehole Data as a Direct Measure of Stress Directions and Variability to Help Constrain the SCEC Crustal Stress Model for Southern California
Name Organization
Joann Stock California Institute of Technology
Other Participants Patricia Persaud
SCEC Priorities 2d SCEC Groups SDOT
Report Due Date 03/15/2016 Date Report Submitted 03/13/2016
Project Abstract
We determined principal stress directions (SH and Sh) in the LA basin, using borehole breakouts ob-tained from well logs in the onshore Long Beach, and Inglewood, and the offshore Wilmington and Hun-tington Beach oil fields down to depths of 3 km. In Inglewood, NE SH orientations occur in most wells south of a NW-striking thrust fault, which are oriented sub-perpendicular to the thrust fault rather than at a consistent angle to the Newport-Inglewood Fault (NIF) zone. An E-W SH direction in two wells likely reflects the stress state of the flower structure in the graben just west of the Inglewood fault. In Long Beach, substantial lateral variation of SH at depths less than 900 m indicates a more variable shallow structure influenced by overthrusting across the Pickler Fault, and merging of the NE Flank Fault and Cherry Hill faults in the topmost 1 km. The large variations in SH in the northern flank of the anticline appear to be related to the N-NW-striking faults that merge with the NIF-Cherry Hill Fault near the anti-clinal crest. Relative changes in the principal stress magnitudes are observed in Huntington Beach. The observed short-length-scale variations in SH direction are attributed to the proximity to faults, fault seg-mentation, or fault overlap. They indicate the likely complexity that may be found in stress fields near other active faults.
Intellectual Merit As far as we know, we are the only group working with borehole breakout data to constrain the SCEC Community Stress Model. This provides a useful complement to the various scales of models being derived from seismicity and geodynamics. We are working with new types of well logs and have updated the methods needed to analyze these.
Broader Impacts As a result of this study we have made contact with other researchers who have access to offshore Santa Barbara data sets. These data sets will be analyzed in our future work. We have established partnerships with more oil field operators and service providers who are learning about what SCEC does, and the importance of their data to the SCEC CSM efforts. We are broadening the participation of underrepresented groups with the involvement of Dr. Patricia Persaud, who is an ethnic minority female scientist.
Exemplary Figure Figure 1.
Caption: Left: Map with Inglewood well locations. Purple lines representing mean SH orientations are scaled with the strength of the breakout (mean resultant length) based on the method of Mardia and Jupp (2000). The yellow-shaded area represents the outline of the anticline based on depths to the top of the Middle Miocene Sentous for-mation that are shallower than 8000 ft (2438 m) from Elliott et al. (2009). The gray thrust fault after Elliott et al. (2009) appears to be a deeper structure. Sizes of the gray circles indicate the number of breakout samples for each well (20 = 3 m). Right: Polar histogram showing SH orientations for all Inglewood wells. Breakouts at depths greater than 2000 m, and less than 2000 m are shaded yellow and red respectively.
Credits: Figure produced by Patricia Persaud.