Though the deep creep may sound like a horror film, it is quite the contrary. It describes a seismic discovery that shakes up current earthquake prediction models and impacts the lives of every person in the Southern California region.
The deep creep constitutes the thousands of small earthquakes that occur 6 miles below us in the San Bernardino Basin.
The deep creep was discussed in Newsweek last month as they reviewed a research study published in the Geophysical Research Letters. Researchers emphatically state scientists should not use information produced by small earthquakes near the San Andreas (SAf) and San Jacinto faults (SJF) to forecast major earthquakes.
Scientists have been digging deeper into the complex fault structures of the SJF and SAf in the San Bernardino Basin. This basin shows movement that is not representative of expected horizontal slip, as many of the earthquakes have also exhibited vertical movement.
Scientists use crustal deformation models to demonstrate that vertical movement can be produced as the SJf continually creeps at depths of 10 km (6 miles), while the SAf is constantly locked with no sign of movement at similar depths.
Dr. Fryxell, Professor of Geology at California State University San Bernardino (CSUSB), addressed this current research in an interview on this topic.
Q. Dr. Fryxell, can you share your thoughts on how this vertical movement happens in the San Bernardino area?
A. The top 8-10 miles of the crust of the earth, is generally cold and brittle rather than malleable.
Imagine pressure pushing on a brittle surface; when the energy builds up and finally releases, the surface can crack or break, and the movement created can be vertical.
At greater depths, more than 10 miles below the surface, the rocks are warmer, so they behave more like cookie dough, which is malleable, so they do not store stress but are more flexible.
The two faults are not quite parallel, and behave differently, as one is continually moving at depths greater than 6 miles (SJf), while the other locked to depths of 12 miles (SAf).
The findings of this study demonstrate that the many small earthquakes that occur regularly adjacent to and between faults can have a different style of deformation than the large ground rupturing earthquakes produced along active faults, thus the challenge of forecasting major earthquakes is increased.
Q. Moving on to basic safety concepts that we should employ on campus relative to earthquake preparedness – what is your advice should a major earthquake occur while classes are in session?
A. The timing of this interview is very good since the Great California Shakeout will be held at CSUSB on October 18 at 10:18 a.m.
Basic safety precautions will be discussed by faculty in each of the classrooms and lecture halls. Duck and cover when possible; and the most important safety precaution we can each employ is to have access to drinkable water in our homes, workplace and car.
At home, you should have enough water to sustain each person for 4-5 days should a major event happen – keep in mind, it is not if a major earthquake will occur in our region, but when.
Q. Can you please share the details of your San Andreas fault hike for this year?
A. The hike will be the same day as the Great Shakeout on Thursday, October 18 starting at 9:30 a.m.
We welcome everyone to come and learn more about the San Andreas fault as we hike to the fault. Remember to wear comfortable clothes and shoes; we will meet outside the Biology Building at 9:30 a.m.
We appreciate the time Dr. Fryxell spent in reviewing the deep creep with us. Be prepared and ready, as we now better understand why it’s not if, but when a major earthquake will happen beneath us.