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Group 2 – SoSAFE | Poster Abstracts
Southern San Andreas Fault Evaluation (SoSAFE)
2-043
AN OVERVIEW OF THE NCALM ALSM OBSERVING PROGRAM FOR THE
UNAVCO SOUTHERN CALIFORNIA (SOCAL) PROJECT. Carter W, Shrestha RL, Sartori
M, Schofield S, and Slatton C
During the period of April 2, to April 24, 2008, the National Center for Airborne Laser Mapping
(NCALM) collected airborne laser swath mapping (ALSM) observations along approximately 900
kilometers of major fault lines in southern California (SoCal). Funding for the project was provided
by UNAVCO, and UNAVCO and Ohio State University personnel participated in the field
operations.
All of the SoCAl ALSM observations were collected with an Optech Gemini system, during 19
flights, totaling some 60 hours of flying time. The widths of the corridors covered varied from 1.2
km to 6 km, in accordance with project specifications set by UNAVCO. The nominal flying height
was 750 meters above local ground level, laser pulse rates were set at 70 or 100 kHz, and the
scanner was generally set at 40 Hz and a scan angle of 25 degrees (on both sides of nadir). The
flying height, laser pulse rate, and swath-to-swath overlap resulted in a nominal point density of 6
points per square meter. The most challenging problem encountered during the data collection was
relatively strong seasonal winds, which caused several planned flights to be delayed or canceled.
The NCALM aircraft, a Cessna an inline twin-engine aircraft, was equipped with two GPS
receivers, each connected to separate antennas: a rack mounted Trimble BD950 GPS Receiver
Module connected to a dual frequency high gain (35 db)Aero-antenna, and a Topcon GB 1000
receiver connected to an Aero-antenna with a 40.0 db amplifier. The Topcon receiver and
associated antenna were provided by OSU. The two receivers and antennas were installed on the
aircraft to evaluate their relative performance, and to minimize the loss or degradation of the final
ALSM data caused by poor aircraft GPS observations. All of the aircraft trajectories used by
NCALM to reduce the SoCAL ALSM observations were generated by Gerald Mader, NOAA, using
the latest version of his kinematic GPS processing software. Mader typically used 4 to 6 ground
base stations, from which he independently computed trajectories. The trajectories were compared
and examined for any unusual differences, and then combined to form the final trajectory for each
flight.
The SoCAL ALSM observations were reduced following standard NCALM computing and quality
control procedures, filtered, and divided into tiles. Both the point cloud and gridded data are
available and researchers wanting to obtain data for their research should contact UNAVCO.
2-044
SLIP ALONG THE SAN ANDREAS FAULT ASSOCIATED WITH THE GREAT 1857
EARTHQUAKE BETWEEN CHOLAME AND PINE MOUNTAIN, DERIVED FROM
“B4” LIDAR HIGH RESOLUTION TOPOGRAPHIC DATA Zielke O, and Arrowsmith JR
The definition of fault segments (e.g., Cholame or Carrizo segment) along the southern San
Andreas Fault (SAF) is based on the distribution of surface slip during the great 1857 earthquake.
Amount and distribution of slip along the rupture are also required to estimate the magnitude of
this event and are used to estimate average recurrence intervals of large earthquakes. The classic
study by Sieh (1978) -examining aerial photographs and traversing most of the surface rupture-
revealed offsets ranging from 3.0 to 9.5 meters along the 300 km long, central part of the 360 to 400
km long surface rupture. He found that the variation is broadly systematic, with uniform slip along
2008 SCEC Annual Meeting | 161