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South Coast Geological Society September Meeting

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Dave & Buster's

20 City Boulevard West

#g1

Orange, CA 92868

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Event description
SCGS Meeting with Dr. Ken Hudnut: "Cross-Fault Interaction in the July 2019 Ridgecrest Earthquake Sequence, Southern California"

About this Event

South Coast Geological Society welcomes you to join our monthly meeting on Monday, September 16th at Dave & Buster’s, Orange, CA. We are thrilled to host guest speaker, Kenneth Hudnut, Ph.D., Science Advisor for Risk Reduction for the U. S. Geological Survey (USGS). Dr. Hudnut will present his talk "Cross-Fault Interaction in the July 2019 Ridgecrest Earthquake Sequence, Southern California."

Speaker:  Hudnut, K.W. (USGS)  --  (co-authors; J. Hernandez, E. Haddon, D. Mencin, J. Lozos, R. Harris, L. Seeber and J. Pacheco)

Abstract:

The July 2019 Ridgecrest earthquake sequence in southern California marked the intersection of two antithetic regional Holocene active fault systems, the northeast-striking, left-lateral boundary between the Sierra Nevada and the Mojave blocks, and the northwest-striking, right-lateral eastern boundary of the Sierra Nevada block. Two large strike-slip ruptures 34.3 hours apart occurred on intersecting, nearly orthogonal, vertical faults during the Ridgecrest sequence. The first significant event (M 6.4) in the 2019 sequence ruptured a northeast-southwest oriented left-lateral “cross-fault” and the second event (M 7.1) initiated its rupture 13 km northwest of its soon-to-be intersection with the cross-fault, then ruptured bi-laterally, towards both the northwest (for 18 km) and southeast (for 30 km) with predominantly right-lateral slip. We previously advanced an hypothesis called the “cross-fault triggering mechanism” to explain the sequence of events, and especially the inter-event delay and stress triggering effect, associated with the Elmore Ranch – Superstition Hills earthquake sequence of November 1987. Here, we explore whether that mechanism, or a variant, may potentially also be applied to understanding the 2019 Ridgecrest earthquake sequence. Strong similarities are evident between the 1987 and 2019 sequences; both seemed to involve cross-fault interaction, but not in identical ways. Differences include, 1) the pattern of seismicity between the times of foreshock and mainshock in each sequence, that is, inter-event seismicity delineated an “I” shape in 1987, but an “L” shape in 2019, and 2) the mainshock in 1987 broke unilaterally to the southeast, away from the intersection with the cross-fault, whereas in 2019 the mainshock ruptured bilaterally away from an epicenter that lay 13 km northwest of the cross-fault’s intersection. The 2019 events’ magnitudes are larger and the sequence is better imaged by new technologies that were (in some cases) not yet available for the 1987 sequence, and there appears to be greater inherent complexity in the 2019 sequence than in 1987. From this sequence and the various new data to be shown on the sequence of surface faulting, first in the M 6.4 and then in the M 7.1, we may improve understanding of short & long-term fault interactions, not only in southern California, but in general.

Speaker Information:

Dr. Ken Hudnut led aerial reconnaissance, field investigations and airborne imagery during response to the 2019 Ridgecrest earthquake sequence. He has studied earthquakes for the U. S. Geological Survey (USGS) since 1992, and received awards for distinguished service and leadership from the American Geophysical Union and U.S. Department of the Interior. He received his Ph.D. from Columbia in 1989 and A.B. (high honors) from Dartmouth in 1983.

Meeting Cost: Members $30; Non-members $35; Students/Professors $15

Reservation: Please make your reservation online no later than NOON, Monday, September 1st. Walk-ins welcome, reservations preferred.

Meeting Schedule: 6:00 PM – Social Hour; 6:30 PM – Dinner Buffet; 7:15 PM – Announcements; 7:30 PM – Presentation; 8:30 PM – Questions/Meeting Adjourned

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Date and Time

Location

Dave & Buster's

20 City Boulevard West

#g1

Orange, CA 92868

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Refund Policy

Contact the organizer to request a refund.

Eventbrite's fee is nonrefundable.

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