Great Place to Build a Tunnel!
1. Information on the Raymond Fault
http://www.digplanet.com/wiki/Raymond_Fault
San Gabriel Valley area
Los Angeles–Ventura areas
External links
2. Significant Earthquakes and Faults
Chronological Earthquake Index
http://www.data.scec.org/significant/chron-index.html
Pasadena Earthquake
Type of Faulting: left-lateral strike-slip, with very minor
reverse motion
Time: December 3, 1988 / 3:38 am PST
Location: 34° 8.47' N, 118° 7.96' W Directly below the city of Pasadena.
Magnitued: M
L5.0
Fault Involved: Raymond fault
Depth: 15.6 km
Apart from its effects on local residents, this quake was notable for
a few seismological details. First, it was followed by an unusually
small number of aftershocks for a quake of its magnitude, the largest of
which was hardly noticable -- only a magnitude 2.4 (unless the
Montebello earthquake is considered an aftershock of this event). Second, it served to bring the debate over the sense of motion of the
Raymond fault closer to an end, by providing a clear example of left-lateral movement most likely located along that fault.
(Many of us remember the Pasadena Earthquake: a whole lot of shaking going on! After this quake, there have been at least 42 quakes of significance in the Southern California area, including ones widely felt in the Pasadena area: 1991, Sierra Madre, 5.8; 1992, Landers, 7.3; and 1994, Northridge, 6.7. Before the Pasadena Earthquake, don't forget the North Palm Springs Earthquake, 5.6, and the Whittier Narrows Earthquake, 5.9. Also, don't forget that the rupture of the San Andreas Fault, the Big One, is long overdue--Isn't that the one with a branch to the Raymond Fault?--with research showing that it is capable of a magnitude 8.1 earthquake [see http://articles.latimes.com/2010/oct/10/local/la-me-san-andreas-20101010 and numerous other articles].)
3. 710 Study Geotechnical Analysis
The convergence of the Peninsular Ranges and the Transverse Ranges has resulted in a very complex geologic structure. As the northwest vergent blocks of the Peninsula Ranges interact with the south vergent Transverse Ranges, a series of new structures has formed to accommodate the collision, including east-west compressional folding and thrusting and east-west trending left lateral faulting to shunt structural blocks off to the west. The San Gabriel Basin is a large down-warp created by regional north-northeast to south-southwest directed compressional geological forces that have uplifted the San Gabriel Mountains and folded the rocks in adjacent hills. Although they are called blind, these contractional thrust faults do express themselves at the surface by the uplift of the hills and valleys within the study area. The Elysian, Repetto, and San Rafael Hills in the western part of the study area are primarily a result of late-Quaternary-age folding and uplift (less than about 500,000 years old). The faults and folds in the hills largely trend southeasterly from the Santa Monica Mountains to the Puente Hills and are commonly referred to as the Elysian Park Fold and Thrust Belt (EPFT). Known active surface faults in the SR 710 Study area are the Raymond and Alhambra Wash faults. The Eagle Rock and San Rafael faults are generally considered to be potentially active because there is inadequate evidence as to their recency of activity.
Local Geologic Setting
Regional Faulting
The surface faults of greatest significance to the project are described in detail as follows. They include the Raymond fault, the Alhambra Wash fault, the Eagle Rock fault, and the San Rafael fault. The Raymond fault is the major active fault in the project area. It is a left-lateral, reverse-oblique fault that dips steeply (approximately 80 degrees) to the north. It extends southwesterly from the Sierra Madre Fault Zone at the base of the San Gabriel Mountains through the communities of Monrovia, Arcadia, San Marino, and Pasadena to the Raymond Hill area of South Pasadena, where the Raymond fault trends more westerly through the communities of South Pasadena, Highland Park, and possibly into Los Angeles for a length of 12 to 15.5 miles. The most-recent major surface rupture on the Raymond fault occurred sometime about 1,000 to 2,000 years ago and the recurrence interval for surface rupturing events may be about 3,300 years.
(Odd that the report doesn't mention to Pasadena Earthquake in 1988 along the Raymond Fault. My comment.)There is little consensus on the rate of slip, with estimates varying from 0.1 to 0.4 millimeters per year (mm/yr) up to 1.5 mm/yr. Earthquake magnitude estimates are moment magnitude (MW) 6.0 to 7.0, with 6.7 preferred (an event that would generate 3 to 5 feet of displacement). The State of California (California Geological Survey [CGS]) has established an Alquist-Priolo Earthquake Fault Zone (APEFZ) along the Raymond fault from the San Gabriel Mountains in the east to near the intersection of Avenue 50 and York Boulevard on the west.
The Alhambra Wash fault is a short northwest-southeast-trending fault in the southern part of the San Gabriel Valley that steps the Whittier fault northward. The surficial expression of the fault segment is approximately 1.5 miles long extending from SR 60 on the southeast to San Gabriel Boulevard on the northwest. The fault is designated as an APEFZ and, therefore, is considered to be active. The potential for surface displacement on the Alhambra Wash fault is poorly known but unpublished work has confirmed multiple late Pleistocene to Holocene ruptures. The maximum magnitude of an event on the Alhambra Wash fault could be about 6.25 if it ruptures separately, but it likely ruptures in larger events with the Whittier fault. The potential for surface rupture displacements along the Alhambra Wash fault would be expected to be lower than for the Raymond fault.
The San Rafael fault trends along the southerly side of the San Rafael Hills across the Arroyo Seco then along the north sides of Grace and Raymond Hills in southwestern Pasadena (Lamar, 1970). To the northwest, the fault apparently dies out north of the Eagle Rock fault as a series of disjointed strands in the basement complex of the San Rafael Hills. It has been observed to dip northeast at 80 degrees with basement rock to the north against Tertiary-age sediments to the south. The kinematics and recency of activity for this fault are unknown. The San Rafael fault is believed to merge with the Raymond fault near Lacy Park in San Marino. The fault is not known to be active; however, a recent geotechnical study at the Blair International Baccalaureate Magnet School identified subsurface faulting in seismic imaging, the age of which is unknown and still under study.
The Eagle Rock fault, mapped as an eastward continuation of the Verdugo fault, lies between the San Rafael and Raymond faults (Lamar, 1970). Southeast of the San Rafael Hills, the fault may be expressed by irregular terrain in a nearly flat surface of overlying terrace deposits. The fault is well exposed where it separates granitic rocks from conglomerate-breccia of the Topanga Formation west of Arroyo Seco. The fault appears to merge with the Raymond fault at Raymond Hill. A combined rupture of the Verdugo and Eagle Rock faults is the most likely scenario for the maximum earthquake magnitude on the Eagle Rock fault.
Numerous additional faults are mapped (Lamar, 1970) in the southwestern part of the study area, forming a complicated region of intersecting faults and fault-bounded blocks. The largest of these faults corresponds to the trace of the northwest-trending Highland Park fault. The Highland Park fault trends for approximately 6.5 miles from Monterey Park through Alhambra and El Sereno to Highland Park. The Highland Park fault appears to terminate against the western continuation of the Raymond fault in the vicinity of York Boulevard. The Highland Park fault is not considered by the CGS (2002) and California Division of Mines and Geology (1977) as active. The Highland Park fault also has not been included in the Uniform California Earthquake Rupture Forecast, Version 2 (UCERF2) catalog.
4. Ken Hudnut, Cal Tech Geophysicist, on the 710 Freeway Tunnel:
www.ci.pasadena.ca.us/WorkArea/linkit.aspx?LinkIdentifier...
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710 freeway – proposed tunnels and related earthquake issues. Ken
Hudnut, Ph.D. Geophysicist ... 710 tunnel alternatives & faults ...