Thursday, July 4, 2019

Remembering Donal M. Ragan

Professor Emeritus of Geology Donal M. Ragan passed away in February 2019. Unfortunately, I had lost some contact with him in the last years. However, I was first hired on in 1995 at ASU to take Don's position (from which he had retired) and teach Structural Geology. He was still active, working on his book and so he came by often to talk with me and my students (especially George Hilley). Don and his wife Janne were also kind to have me over for dinner occasionally. They were very generous. This memory of Don is incomplete, but I wanted to capture a few thoughts and recollections.

This is the only picture I could find of Don. He is there on the left (along with Lee Amoroso, Jeri J. Young, and George Hilley) during a field trip to the Carrizo Plain in the late 1990s.

I don't have all of Don's biography. I recall he was born in southern California and maybe went to Occidental College. He was in the Army and talked about the discipline and repetitiveness of learning how to dissassemble and assemble a machine gun. He went to the University of Washington where he worked on deformation in the Twin Sisters Dunite. He was at Imperial College where he worked with John Ramsay. He moved to the University of Alaska (UAF) and published on deformation associated with glacial ice (e.g., Ragan, 1969). He moved to Arizona State University in 1965 at the behest of Prof. T. L. Péwé who had been hired to be chairman and who knew Don from UAF.

We worked a fair bit with Don on MATLAB implementations of his exercises and ideas. A couple are here. And, he was an avid LaTEX user having had problems in the 3rd Edition of the book when he did not have good control over the copy editing and production. He taught us about dashes and quotes.

In 2000, Don taught a series of lectures on Structural Geology. I helped a bit mostly as coordinator and provider of moral support. These reflected the development for the book and all I really have are the handouts and figures for transparencies and a few notes:

Don was outspoken about quantitative approaches in structural geology: "Despite all this effort one can still find in professional articles statements that violate basic laws of physics and in some current textbooks there are important omissions, misstatements, misinterpretations and errors when dealing with structure making processes." (from his review of The Life of Frank Coles Phillips).

I worked with him for a while on the 4th edition of the textbook, but did not contribute enough in time to stay a coauthor. Nevertheless, I learned so much from Don and did what I could to apply those lessons in the GLG310 Structural Geology and the GLG510 Advanced Structural Geology courses. We talked often about how to teach structural geology and how to bring more quantification and precision to it. We followed the developments of the structural geology textbook (FSG) of Professor David Pollard at Stanford. Don and I wrote a short review of an early version of a manuscript on kinematics and mechanics here. Don wrote a blurb for the book: "This is the best book on structural geology in a long time. It is both rooted in classical mechanics and visionary. In their characteristic fashion, Pollard and Fletcher lay out the physical concepts and tools needed to understand the structure-making processes and give many examples of their use. If you have any interest at all in the subject read this book, but be prepared to work. You’ll be glad you did."

M 7.1 - 17km NNE of Ridgecrest, CA (was Accumulating links for: M 6.4 - 12km SW of Searles Valley, CA)

I have prepared a summary presentation on the earthquake sequence. The July 17 versions here here: PDF and PPT. They are comprised of material harvested from publicly accessible sites, so I am hoping it is ok to redistribute in this form; I have provided attribution. Let me know if something needs to be udpated.

And then the the 4th of July event was a foreshock. As I mentioned below, there was a 9% probability from the USGS that the July 4th event would be followed by something larger, and it actually was. I hope that people are ok; will take until the morning to have a better sense of damage and injuries.

I am regularly updating this page, so occasionally refresh.

Tonight's event is clearly part of the same sequence, although this was along the NW-trending section (and was right-lateral). This is an impressive conjugate pattern (right lateral along the NW orientation and left lateral along the NE orientation). Both orientations and senses of motion are consistent with the overall shear zone deformation in the area. It looks to have ruptured across the Highway 178. There are also lots of mass movements in the area (lots of dust kicked up in videos, and also rock falls onto the roads, etc.).

This event was an M6.9 refined from the M7.1 initial estimate. This is a half magnitude unit larger so it was ~10x more energy, hence the broader felt extent (more people in Phoenix and Las Vegas noted it; e.g., my colleagues and my sister...). If you felt (or not) good to fill out a report. This one will certainly be followed by many aftershocks, and there is again a small chance that a larger one could follow. (Omori’s law: ~logarithmic decay in time for event rate (ratio of big to small aftershocks stays the same.) But you can also think of these events close in time and space as epidemics (epidemic type aftershock sequence, most that follow are smaller, but sometimes a bigger one can follow as we have seen). An event of the July 4 size could be an aftershock now...

Locations from and the focal mechanism from USGS. Compare this with the similar one below.

ASU recording:; thanks to John West and Ed Garnero


A 4th of July earthquake with an impressive conjugate aftershock pattern in the Eastern California Shear Zone.

Locations from and the focal mechanism from USGS.

Deferring to USGS/CGS colleagues for the real interpretation, but this looks to be consistent with maybe a primary rupture on one of the trends and then aftershocks climbing up the other. Given the magnitude and length scaling, for the moment, I am going to guess the rupture was on the NE trend and would be left lateral with a few 10s cm cracking (based on image below could be Little Lake Fault zone?). This is also consistent with the conjugate fault pattern mapped in the region (see NW and NE-trending faults on map below).

Update about 2 pm: indeed, decimeter-scale rupture, left lateral, crossing Highway 178. See this tweet. The location is 35.644167, -117.535833--close to where the aftershock trace.

It has a vigorous aftershock sequence which is consistent with expectations. The USGS is employing Operational Earthquake Forecasting to provide probabilistic statements about expected aftershocks in the region.

Locations and active faults from USGS. Fractured Hwy 178 from @neotectonic

It was widely felt in California: USGS DYFI. This is a good reminder about earthquake safety.

Useful links: