Ahrens, Thomas J.

Henyey, Thomas L.

Leary, Peter C.

Teng, Ta-Liang

Caltech Authors - Main

A MULTI-PURPOSE CRUSTAL STAIN OBSERVATORY, 
DALTON TUNNEL COMPLEX, SAN GABRIEL MOUNTAINS
Thomas L. Henyey
Ta-liang Teng 
Peter C. Leary
Earth and Space Sciences Institute 
University of Southern California 
Los Angeles, California 90007
Thomas J. Ahrens
Seismological Laboratory
California Institute of Technology
Pasadena, California 91109
USGS CONTRACT NO. 14-08-0001-18339 
Supported by the EARTHQUAKE HAZARDS REDUCTION PROGRAM
OPEN-FILE NO. 81-280
U.S. Geological Survey 
OPEN FILE REPORT
This report was prepared under contract to the U.S. Geological Survey 
and has not been reviewed for conformity with USGS editorial standards 
and stratigraphic nomenclature. Opinions and conclusions expressed 
herein do not necessarily represent those of the USGS. Any use of trade 
names is for descriptive purposes only and does not imply endorsement by 
the USGS.
U. S. C. Geophysics Laboratory Technical Report #80-11
A MULTI-PURPOSE CRUSTAL STRAIN OBSERVATORY, 
DALTON TUNNEL COMPLEX, SAN GABRIEL MOUNTAINS
(September 1, 1979 to September 30, 1980)
Thomas L. Henyey 
Ta-liang Teng 
Peter C. Leary
Earth and Space Sciences Institute
University of Southern California
Los Angeles, California 90007
Thomas J. Ahrens
Seismo"logical Laboratory 
California Institute of Technology 
Pasadena, California
November, 1980
FINAL TECHNICAL REPORT SUBMITTED TO THE 
U. S. GEOLOGICAL SURVEY 
by the
EARTH AND SPACE SCIENCES INSTITUTE 
UNIVERSITY OF SOUTHERN CALIFORNIA
Contract No.: #14-08-0001-18339
Principal Investigators: Thomas L. Henyey
Associate Professor, Geophysics
Ta-liang Teng 
Professor, Geophysics
Government Technical Officer: Karen Ward
Title of Work: A Multi-Purpose Crustal Strain Observatory,
Dalton Tunnel Complex, San Gabriel Mountains
Effective Date of Contract: September 1, 1979
Contract Expiration Date: September 30, 1980
Amount of Contract: $139,981
Report Period: September 1, 1979 to September 30, 1980
This work is sponsored by the U. S. Geological 
Survey under Contract #14-08-0001-18339
The views and conclusions contained in this document 
are those of the authors and should not be interpreted as 
necessarily representing the official policies, either 
expressed or implied, of the U. S. Government.
November, 1980
University of Southern California Geophysical Laboratory 
Techical Report 80-11
PROJECT STATUS
The first year U.S.G.S. contract for the Dalton Observatory, a U.S.C.- 
Caltech joint project, has been completed. Work on the facility has been 
completed. Several instruments are on line. Work on additional instrument 
installation is continuing. Progress is outlined below:
Facilities:
1) Permits for extended use of the tunnel and construction 
of on-site facilities have been obtained from the Los 
Angeles County Flood Control District.
2) The tunnel has been "barred down" and the loose debris 
removed by a commercial contractor. Low spots in the 
floor have been filled and the drainage improved.
3) The tunnel has been inspected by OSHA and deemed safe 
for general use as proposed.
4) An electronics blockhouse and access bridge have been
designed and constructed. This work has been a cooperative 
effort by personnel at U.S.C. and outside contractors.
5) AC power has been installed.
6) Piers have been constructed.
7) Telephone data lines should be ready early in fiscal year 1981. 
Equipment: Installation of equipment is proceeding according to plans 
(Figure 1). Present instrument status (see Table I) is as follows:
1) Lacoste tidal gravimeter - in calibration; final hook-up awaits 
a re-zero switch.
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TABLE I
Instruments Scheduled for Installation at 
Dalton Observatory During Current Year
Instrument
1. Acoustic Emissions Recorder
2. Continuous Radon Counter
Note: M. Shapiro is present operating 
a continuous 3-counter at Dalton
3. LaCoste H-7-G Gravimeter with 0.001 milligal 
resolution.
4. Drill hole with borehole water level, turbidity 
and temperature sensors.
5. Fluid level tiltmeters (orthogonal pair)
6. Carbon fiber strainmeter (orthogonal pair)
Two Press-Ewing long-period seismometers w/D.C 
transducers (orthogonal pair of garden-gate 
tiltmeters).
Kinemetrics bubble tiltmeter
9. Ground thermisor array
10. Meteorological Station
11. Recorders: 2 TIMs
2 digital cassette recorders
1 multipoint recorder
12. Strong motion accelerographs - Existing units 
at both the observatory and Dalton Dam
Person Responsible 
Teng 
Teng
Henyey 
Henyey
Leary 
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Bilham
Miller 
Ahrens
Miller 
Ahrens
Leary 
Henyey
Leary
Nickerson 
Manov
CDMG
2) Acoustic emission recorder - installed.
3) Two carbon fiber strainmeters - installed.
4) Two fluid level tiltmeters - installed.
5) Two bubble tiltmeters - installed.
6) Two Press-Ewing long period seismometers w/D.C. transducers 
(garden gate tiltmeters) - installed.
7) Ground temperature monitoring array - installed.
8) Meteorological station - installed.
9) Borehole for water level transducer - not yet drilled, 
instruments standing by at U.S.C.
10) Continuous Radon monitor (a-counter) - standing by at U.S.C.
(M. Shapiro of Caltech is currently monitoring Radon (3-counter) 
near Dalton Observatory in a shallow well).
11) Telemetry interface modules, digital and analog recorders - 
standing by at Caltech and U.S.C.
12) Vibrating string experiment (Bruce Clark, Leighton Assoc.) - 
two holes drilled, instruments being installed.
13) Dry tilt array (Art Sylvester, UCSB) - initial lines to be laid
out in the fall, 1980. 
RESULTS
Two pair of Bilham-King carbon fiber strainmeters are presently operating 
in southern California. One pair (an orthogonal NW-NE pair, 105 and 195 ft. 
long, respectively, in Dalton Canyon north of Glendora) were set up in mid-June 
1980 and have given stable data since installation. The other pair (parallel; 
east-west orientation; 80 ft. and 60 ft. long located in a shallow mine just 
north of Bouquet Reservoir) has been operational since December 1978. One unit 
has given continuous records to the present; the second has been repaired twice.
A. Pal ton Strainmeters
Dalton Tunnel (Figure 2) was equipped with massive concrete 
piers anchored to the tunnel walls by numerous ribs of 3/4" re- 
inforcing steel epoxied to the rock to depths of 18". The two 
strainmeter mounts were fixed to the piers with stainless steel 
anchors and epoxied in place. The instruments have shown no 
tendency to drift after the first week.
Because Dalton Tunnel is still being regularly visited by 
persons installing instrumentation, we have not processed the 
long-term records. A sample short-term (^ 1 wk) record is repro- 
duced in Figure 3. The new Hebrides earthquake excited a sizable 
response in the NE (195 ft.) instrument (Figure 4) but not the 
NW (105 ft.) instrument. Since the relative azimuth of source 
and receiver is NE, the preferential excitation on the NE instrument 
may reflect strong Rayleigh wave energy and weak Love wave energy 
along the azimuth.
B. Bouquet Strainmeters
Figure 5 shows the two Bouquet Strainmeters tracking between 
December 1978 and April 1979. Subsequently BQS1 experienced an 
episode of E-W tension in the period covered by the trilateration 
anomaly of Savage. Figure 6 extends the BQS1 data through March 
1980. Unprocessed records for June and July, 1980, show the ex- 
tensional recovery of March 1980 to be continuing. BQS2 has 
experienced repeated problems with its end mounts and has not re- 
turned stable data since spring of 1979.
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A Multi-purpose crustal strain observatory, Dalton Tunnel complex, San Gabriel Mountains

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A Multi-purpose crustal strain observatory, Dalton Tunnel complex, San Gabriel Mountains

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