| Serving professionals in engineering, environmental, and groundwater geology since 1957 | |
|
MONTHLY DINNER MEETING
(joint meeting with SCGS)
DATE:
Tuesday, July 15, 2003
LOCATION: Wyndham Garden Hotel, 3350 Ave. of the Arts, Costa Mesa
TIME: 6:00 pm--Social Hour, 7:00 pm—Dinner, 8:00 pm--Talk
RESERVATIONS: Call Leighton & Associates (949) 250-1421 ex. 570
by noon, Friday,
July 11. PLEASE INDICATE YOUR CHOICE OF SALMON or
LONDON BROIL when you call in.
COST: $22 per person with reservations, $27 at the door, $12 for students.
SPEAKER: Eldon Gath
TITLE: Uplift of the Puente Hills and Santa Monica
Mountains
ABSTRACT
The Santa Ana Mountains (SAM) are a 1.7 km high mountain range that have
not yet been provided with an uplift mechanism. The uplift issue is not
just geological curiosity, but it could be of extreme importance to the
safety of the citizens of Orange and Riverside counties. Recent geomorphic
mapping and analysis are providing some constraints on patterns and rates
of uplift, and attempting to shed light on the uplift mechanism and seismic
hazard implications. This work is using a new method of quantitative analysis
from the Puente Hills based on relationships between drainage basin area
and age, then applied to the Santiago Creek drainage basin. In the Puente
Hills, the basin age was calculated by measuring the right-lateral strike-slip
displacement of each basin’s primary stream, and regressing it against
the basin’s area.! Because the Whittier fault’s slip rate
is known (2.5 mm/yr), the age of the channel can be calculated by retro-deforming
it.! So, if you calculate the basin area, you can calculate the age of
the initiation of the stream forming the drainage basin. The PH also have
three fill terraces and three higher erosional surfaces. From this analysis,
the Puente Hills have been rising 0.4 mm/yr since their emergence ~1 Ma.!
The SAM have three well developed erosional surfaces preserved on them,
as well as a suite of four fluvial fill terraces preserved in Santiago
Creek, a drainage trapped between the uplifting SAM and a parallel Loma
Ridge. By correlation of the terraces with the marine eustatic sea level
curve, (similar to the San Joaquin Hills) we were able to estimate a 0.3
mm/yr uplift rate for the SAM and an emergence age of ~3.6 Ma.! Santiago
Creek formed ~2.4 Ma in conjunction with the initiation of the Loma Ridge
structure, a hanging wall structure that formed in response to compressional
buckling of sedimentary strata on the flanks of the uplifting Santa Ana
block. Hanging wall block faulting appears to have deflected Santiago
Creek northerly ~1,200 m along five discrete block margin faults. The
termination of the Elsinore fault into the Chino and Whittier faults leaves
at least 1-2 mm/yr of north-vergent strain unaccounted for. We speculate
that this missing strain is being transferred into uplift of the SAM,
with complex interaction among other northvergent structures in the southern
California area. Come, hear, argue.
Biography
Eldon Gath is the President of Earth Consultants International (ECI),
a geological consulting firm formedin 1997. Eldon has nearly 25 years
of professional consulting experience with southern California firms Pacific
Soils Engineering and Leighton and Associates before forming ECI.! He
received his BS in Geology from the University of Minnesota in 1978, and
has been in and out of all southern California graduate schools ever since.!
Eldon is a past president of the South Coast Geological Society, a past
national president of theAssociation of Engineering Geologists, and is
currently serving on the National Research Council committee to develop
a research agenda for the National Earthquake Engineering Simulation program.!
This talk is based on research for his PhD at UCI, led by Dr. Lisa Grant
of the Dept. of Environmental Analysis and Design, and admirably assisted
by Eric Runnerstrom.
|
|
| |
|