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Engineering Seminar: Los Alamos Seismic Rupture Directivity Study of PF-4

April 2, 2013
Time: 3:30 - 5:00
Location: Research Park, Rm 203A

Speaker: Eric R. MacFarlane
Design Engineering (ES-DE)
Los Alamos National Laboratory

Abstract: T
he presentation will discuss historical seismicity in New Mexico and the seismic hazard local to Los Alamos. Historic evidence of earthquakes, geological investigations performed at LANL, and inputs to the seismic hazard at LANL will be presented.

The concluding portion of the talk will focus on a Near Source Rupture Directivity study which was performed on the PF-4 superstructure. Near Source Rupture Directivity is concerned with how earthquake rupture direction can influence the frequency content of earthquake ground motion. Rupture Directivity is broadly concerned with two regions relative to the location of the epicenter of an earthquake. If the rupture propagates toward a site, it is considered to be in the forward directivity region. Conversely, if the rupture propagates away from a site, the site is considered to be in the backward directivity region. At sites located in the forward directivity region with close proximity to the epicenter, where the shear wave speed of the soil closely matches the S wave propagation speed, it has been observed that there is significant variation in the event experienced at fault normal sites versus fault parallel sites. The events recorded at fault normal sites can contain what is commonly referred to as directivity pulses. These pulses occur early in an event and deliver the majority of the energy produced by the earthquake. The effect of directivity pulses on LANL structures has been raised by external regulators.

To support the study, a simplified nonlinear structural model of the PF-4 superstructure was developed. The intent of the model was to observe how the dynamic properties of PF-4 could change following significant yielding in the lateral system produced by energy transmitted before or during the arrival of the directivity pulse. This model was subjected to twenty-five earthquake time history recordings, recorded at fault normal sites, scaled to match expected seismic events in Los Alamos. The selected time history records came from the Pacific Earthquake Engineering Research (PEER) data base and are known to contain directivity pulses.

Eric MacFarlane received a Bachelor of Science in Civil Engineering from Iowa State University in 1992 and a Master of Science in Structural Engineering from Illinois Institute of Technology in 1998. Prior to coming to Los Alamos National Laboratory in April of 2011, he worked for nineteen years as a consulting structural engineer on petrochemical, transportation, architectural, and power generation projects.  Eric is now part of the Office of Seismic Hazards and Risk Mitigation and focuses on studying the dynamic behavior of buildings and other structures under seismic loading. Since coming to the Lab, he has primarily focused on assisting with the seismic rehabilitation of PF-4. Eric is a Licensed Professional Engineer (PE) in IL, NM, and NV and a Licensed Structural Engineer (SE) in IL, NV, and UT.


For more information contact the institutional host Chuck Farrar, farrar@lanl.gov, 663-5330.
Please download the announcement here.


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