Serving professionals in engineering, environmental, and groundwater geology
since 1957

***Tuesday, October 14th***
Joint Meeting with the
South Coast Geological Society

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Topic: "A Preliminary Case for Secondary Tectonic Distress in the Epicentral Region of the M6.7 1994 Northridge Earthquake"

Speaker: Dr. Jeffrey A. Johnson, P.G., C.E.G.

Location: Double Tree Club Hotel in Santa Ana. Directions:

Time: 6:00 p.m.-Social Hour; 7:00 p.m.-Dinner, 8:00 p.m.-Presentation

Cost: $25 per person with reservations, $30 without reservations, $15 with a valid Student ID.

Reservations: RSVP by logging on to the SCGS web site
or call Maria Herzberg at 714-412-1502 or Boris Zaprianoff at 949-436-3444.

The 1994 Northridge earthquake occurred on a blind thrust fault below the San Fernando Valley. The SFV is an intermontane basin within the convergent Transverse Ranges. Coseismic rupture, on regional thrusts, contributes to millimeter level convergence across the Transverse Ranges west of the San Andreas. Clearly, with time, the floor of the SFV will deform or continue to deform as a result of regional convergence. The question is can a single blind thrust earthquake produce damaging secondary tectonic distress, at the surface of a deep alluvial valley, and will future distress occur at the same location? The answer appears to be a qualified yes. To better understand the issue street by street reconnaissance level mapping ( 120 km2), of distress to streets, sidewalks, curbs, etc., was conducted in the epicentral region of the SFV. The distress was plotted on 1920s topographic maps, aerial photos from the Fairchild Collection, Whittier College and color aerial photos taken shortly after the earthquake. The location of failed gas and water lines were also collected, from SoCalGas and the DWP, and plotted. Although subtle, observed distress locally exacerbated pipeline failures, may have contributed to fatalities at a Northridge apartment complex and exhibited some similarities with distress noted following the 1971 San Fernando earthquake. Offsets, observed along crack zones, were one to two orders of magnitude less than the estimated meter displacements on the primary fault. However, locally distress appears to correlate with valley floor geomorphic features suggesting similar distress may have occurred during prior earthquakes.
Speaker Brief Biography:
Jeff Johnson has a B.S. in Geology from Cal State Northridge, a M.S. in Geology from UCLA, and a Ph.D. in Engineering from UCLA with a major in Soil Mechanics and minors in Earthquake Engineering/Engineering Geology. Jeff is a registered P.G. and C.E.G. in the state of California. Jeff is a consultant; his firm is Engineering Geology and Applied Seismology, out of San Diego. Since 1969 his career has been divided between research, teaching and consulting. Research has been devoted to the understanding of geological and seismic processes and their potential affects on the performance of engineered structures. Studies, including the adverse effects of landslides, subsidence, differential settlement, near source ground motion, coseismic fault rupture and associated deformation, and liquefaction have been conducted in the United States, Central and South America, the Middle East, and Japan. Current research includes: (1) the origin and stability of deep-seated landslides in the complex and seismically active region along the bend between the Hayward and Calaveras faults; (2) the development of criteria for the identification of seismic exacerbation of cracks in engineered structures; and (3) the relationship between surface distress and damage to buried pipelines and coseismic slip on blind thrusts.