Reflectivity Structure Below the San Fernando Valley from Northridge
Project funded by the National Science Foundation,
Principal Investigator: John N. Louie
Seismological Laboratory, The University of Nevada, Reno
- Apr. 7 1998 USGS NEHRP external research program proposal
``Imaging the Elysian Park Thrust, L.A. Basin, with SCSN Data'',
text and figures in HTML
- View a 1998
Tectonophysics paper by Sergio Chavez-Perez and John N. Louie,
``Crustal imaging in southern California using
earthquake sequences'', v. 286, (March 15).
- View Sergio Chavez-Perez's
1997 UNR Ph.D. Thesis
``Enhanced Imaging of Fault Zones in Southern California From Seismic Reflection
- View our migration of crustal structure along
LARSE line 1 from the 6/28/91 M5.8 Sierra Madre event and aftershocks,
which images the same highly-reflective zone at 15-19 km
seen in the LARSE line 1 explosion survey results.
- View the first 3-d migration results, in a
presented at the 1995 American Geophysical Union Fall Meeting, San Francisco;
and a paper to be
presented at the 11th World Conference on Earthquake Engineering, Acapulco,
- View the extended abstract
of a presentaton at the October 1995 Society of Exploration Geophysicists
Annual International Meeting, Houston.
- View a poster
presented at the September 1995 Southern California Earthquake Center
Meeting, Ojai, Calif.
- View a poster
presented at the 1994 American Geophysical Union Fall Meeting, San Francisco.
- A working list of files and data actively
in use by our research, for local access.
NSF Final Project Report 17 June 1996
NSF Proposal 1 Dec. 1996
SCEC Proposals 10 Dec. 1996
The broad destruction caused by the Jan. 17, 1994 earthquake on a fault
buried below Northridge in the heavily-urbanized San Fernando Valley emphasizes
the immediate need for better understanding of hidden fault systems. This project
will assess the Northridge earthquake source and related geological structures by
applying geophysical techniques borrowed from seismic reflection surveying to
seismic network recordings of the earthquake's abundant aftershocks. The
earthquake occurred on a fault that does not break the surface, but that may
have been evident in oil-industry seismic reflection surveys of the underlying
basin sediments. However, neither industry data nor other existing analyses
unambiguously show how numerous buried and exposed faults may be related at
depth within the basement, or which faults may be more continuous or more
recent, thus presenting greater seismic potential.
This project will elucidate regional fault structures by imaging reflectivity
structure below the Northridge aftershock zone. As in industry seismic-reflection
surveying, imaging of structure through high-frequency reflectivity demands
high-multiplicity data, or a large number of overlapping sources and receivers.
The large number of aftershocks recorded to date by the many stations of the
Southern California Seismic Network (SCSN) provide the required multiplicity
within the San Fernando Valley region. Reconnaissance seismic profiles taken
worldwide have shown that reflection frequencies between 1 and 35 Hz are
particularly sensitive to fault structures in the middle crust. This project will
apply both standard and innovative seismic reflection imaging techniques to the
aftershock data, resulting in three-dimensional images of the location, depth,
and geometry of buried fault systems in the region.
The Data Center at the Southern California Earthquake Center (SCEC) has
230 Northridge aftershocks of magnitude 3.0 or greater on file, having more than10 stations recorded each. In fact, most of these events have more than 100
seismograms recorded at SCSN stations up to 150 km distant. This provides a data
set of between 10,000 and 20,000 seismograms, comparable in multiplicity to a seismic
reflection survey. These data are adequate to define fault geometries below theSan Fernando Valley in 3-d at 0.5 to 1 km precision. Initial processing on data from
a few events, equivalent to a 2-d stacked seismic section, identifies reflectivestructures at about 15 and 19 km depth below the epicentral area. This project
will establish a data pipeline from SCEC to UNR to process data from all 230 andany further aftershocks, and investigate filtering and signal-processing strategies
for best reflector imaging from the seismic data. Then this project will employboth standard common-midpoint stacking as well as advanced nonlinear diffractiontomography to produce 3-d reflector geometries below the region. These will be
published in the Northridge data report as well as made available via the Internet.