The Advisory Committee in Seismology has pleasure in reporting the

continued progress of its study of California earth movements during

the year 1924-1925 without essential change of plan. A considerable

amount of geologic work in the study of fault zones has been done during

the year in the Mojave Desert and in Death Valley, the system of

primary triangulation for the detection and measurement of horizontal

displacements has progressed rapidly and effectively, and the development

of suitable instruments for determining the two horizontal components

of local earth movements has progressed to completion. Ground

for a new laboratory has been purchased by the California Institute of

Technology and the construction of the central station laboratory building

upon it has been begun. The laboratory is expected to be occupied

by Mr. H. O. Wood, Research Associate in Seismology, and his associates,

about January 1, 1926. It is hoped that additional stations will also

be occupied before the close of the present calendar year (1925), and

that actual work in what has been happily termed the seismologic triangulation

of California will be successfully inaugurated

Anderson, J. A.

Arnold, Ralph

Buwalda, J. P.

Campbell, W. W.

Day, Arthur L.

Lawson, A. C.

Millikan, R. A.

Reid, Henry Fielding

Willis, Bailey

The year 1925-26 has been one of noteworthy progress in the study

of the zones of movement in California, undertaken by the Carnegie

Institution of Washington and the powerful agencies co-operating with

it. The purpose of these efforts and the definite plan which has been

followed hitherto have been adequately set forth in the earlier reports of

this Committee. It is appropriate that this report should indicate some

of the more conspicuous results which have thus far been attained, for

it is through these that the promise for the future is best appraised.

All of the Annual Reports of the Committee have contained brief

mention of the progress of the detailed study of the southern portion of

the San Andreas rift, the master fault of California, undertaken by Dr.

L. F. Noble, of the United States Geological Survey, and his associates.

This deep fault, active, as Dr. Noble has shown, through long periods of

geologic time, may prove to be the ultimate source and center of the

widespread group of movements which this Committee has set itself to

study. The report is therefore of fundamental importance to any study

of earth movements in this region and of immediate interest to all

American seismologists

Caltech Authors - Main

Report of the Advisory Committee in Seismology

The report of the Advisory Committee for the year ending June 30,

1927, is necessarily brief in content and transitional in character. Development

work in the laboratory has been more or less interrupted throughout

the year by the confusion of dismanteling the equipment at the Mount

Wilson Observatory and removing it to the new Seismological Laboratory

provided by the California Institute of Technology. The equipment

of the various sub-stations about Pasadena and the adjustment of new

apparatus therein has been going on throughout the year, but the continuous

daily record of tremors is still tentative and inadequate because of

the lack of a proper minute-to-minute time service through which to compare

them. Progress in the San Francisco Bay region, which has been

greatly stimulated through the personal efforts of Mr. Willis of this

Committee, is also passing through similar transitional operations, and

Mr. Willis is now absent on a journey around the world in the interest

of general seismology. However, these activities are in themselves adequate

evidence of progress even though we must wait for tangible results

from them until the next and following years

Reid, Harry Fielding

REPORT OF THE ADVISORY COMMITTEE 249 
REPORT OF THE ADVISORY COMMITTEE 
IN SE ISMOLOGY 1 
The report of the Advisory Committee for the year ending June 30, 
1927, is necessarily brief in content and transitional in character. Develop- 
ment work in the laboratory has been more or less interrupted throughout 
the year by the confusion of dismanteling the equipment at the Mount 
Wilson Observatory and removing it to the new Seismological Labora- 
tory provided by the California Institute of Technology. The equipment 
of the various sub-stations about Pasadena nd the adjustment of new 
apparatus therein has been going on throughout the year, but the continu- 
ous daily record of tremors is still tentative and inadequate because of 
the lack of a proper minute-to-minute time service through which to com- 
pare them. Progress in the San Francisco Bay region, which has been 
greatly stimulated through the personal efforts of Mr. Willis of this 
Committee, is also passing through similar transitional operations, and 
Mr. Willis is now absent on a journey around the world in the interest 
of general seismology. However, these activities are in themselves ade- 
quate evidence of progress even though we must wait for tangible results 
from them until the next and following years. 
FAULT ZONE GEOLOGY 
The Committee continues to be indebted to the United States Geo- 
logical Survey for active co-operation i  the detailed study of the fault 
zones of southern California. Dr. Levi F. Noble, whose splendid report 
on the San Andreas Fault last year was the major item of progress re- 
ported by this Committee, is continuing his studies to the south of Cajon 
Pass in the same thorough manner as heretofore. A further report, of 
equal interest with the first, may therefore be anticipated from Dr. Noble 
in the near future. Geological studies in the interest of seismology about 
the San Francisco Bay region have been more or less interrupted because 
of the absence of Mr. Willis in the Orient. 
Reprinted from Year Book No. 26, 1926-1927, of the Carnegie Institution of 
Washington. 
250 BULLET IN  OF  T I IE  SE ISMOLOGICAL  SOCIETY  OF  AMERICA 
TRIANGULATION AND PRECISE LEVELING 
The United States Coast and Geodetic Survey is continuing its work 
in those portions of California which are particularly subject to earth 
movements. The system of triangulation through which horizontal dis- 
placements may be detected is now nearly completed, following the lines 
heretofore described in detail in these reports. It is our belief that the 
fault zones of California are now adequately covered by this triangulation 
net and that slow displacements or local disruption can be accurately 
located through these fixed points and appropriate local measurements. 
During the past winter the entire triangulation net west of the 
Mississippi River has been subjected to a careful scrutiny with reference 
to the appropriate distribution of closing errors in areas surveyed at 
different imes. When this readjustment is completed it is believed that 
all errors in the location of fixed triangulation points will be reduced to a 
minimum. This Committee is particularly interested in this readjustment 
of values because of considerable displacements discovered in the zone to 
the southwest of the San Andreas rift which reach their maximum in the 
vicinity of Santa Barbara and which were at first believed to indicate 
strains in that region sufficient o account for the Santa Barbara earth- 
quake of two years ago. Control measurements have since shown this 
conclusion to be improbable. These strains, however great they may 
eventually be proved to be, apparently had nothing to do with this earth- 
quake. It appears to have been entirely local and no displacement due to 
it which reaches to the main fault zone has been shown. Until these 
adjusted values are known, however, the absolute value of the displace- 
ments detected is still uncertain. Of the progress of the recalculation, 
Major C. V. Hodgson, Acting Chief of the Division of Geodesy, reports 
as follows : 
The adjustment of the triangulation reobserved in the earthquake region of 
California has been delayed in or er that the final readjusted values in the western 
part of the United States could be used for comparison. The readjusted positions 
of the junction stations have now been obtained and the work of adjusting the con- 
necting loop is now in progress. No comparison between the old and the new work 
can be made until the adjusted values throughout the loop have been obtained. It 
is hoped that the adjustments may be finished in the course of two months and then 
the two lists of positions, resulting from the old work and the new, will be pre- 
pared for comparison. Dr. William Bowie, Chief of the Division of Geodesy of the 
United States Coast and Geodetic Survey, expects to prepare a discussion of the 
data compared, after his return from the meeting of the International Geodetic 
and Geophysical Union t  be held in Prague, in September 1927. This discussion 
and the conclusions drawn will be issued in a publication f the United States 
Coast and Geodetic Survey and it should appear some time this coming winter. 
REPORT OF THE ADVISORY COMMITTEE 251 
The present program of the Coast and Geodetic Survey contemplates 
a net-work of precise levels in the southern California fault zone through 
which vertical positions may also be established in sufficient number to 
permit the ready detection of vertical movement in this region. Dr. 
Noble's report of last year furnished abundant evidence of such move- 
ments throughout he recent geological history of the region. Of the 
two-year leveling program of the Geodetic Survey in southern California 
about half is finished; the northern region about Mount  Whitney still 
remains to be completed as soon as the condition of the mountain trail 
permits. 
PUBLICATIONS 
Continuing the administration of the special grant of $5,000 provided 
by the Carnegie Corporation of New York in aid of seismological publi- 
cation, eight reports of current seismologic research, including Professor 
Byerly's full account of the Montana Earthquake of June 28, 1925, have 
been published in the Bulletin of the Seis~cological Society of America 
at the expense of the grant. The total amount expended was $1,301.75, 
the balance remaining on July 1, 1927, is $339.29. 
LABORATORY WORK 2 
At the end of June 1926, it was expected that the new Seismological Laboratory 
at Pasadena would become available within a very short time. Unforeseen con- 
tingencies led to one delay after another, so that authorization to take possession 
of the building and enter upon fitting it up was not given until the middle of Decem- 
ber 1926. These delays, coming in sequence, seriously handicapped the work of 
experimentation and instrument development which had reached a stage where good 
progress was dependent upon facilities provided for in the new quarters, but not 
available in the old. And since the delays came unexpectedly, one after another, the 
straight-forward work of earthquake registration was affected adversely, since 
from week to week it appeared undesirable to initiate new routine or set up new 
experimental pparatus at the old quarters, about o be vacated, to replace experi- 
mental apparatus which had been discontinued and dismanteled there. For several 
months registration was at low ebb. Conduct of work in the new location was 
begun early in January 1927, and this has gone on, increasing as facilities permitted, 
up to the date of this report. Work was continued in the old quarters at the Mount 
Wilson Observatory Office, decreasing in amount as the facilities at the new build- 
ing became available, until the middle of April 1927, when the transfer of all work 
to the new quarters was completed, except for some experimental registration 
which will be continued at the Observatory Office for an. indefinite time. 
The new Seismological Laboratory is situated a little over a mile due west of 
the business center of Pasadena from which it is separated by a high, narrow 
2 Extracted from the report of H. O. Wood, Research Associate in Seismology. 
252 BULLETIN OF THE SEISMOLOGICAL SOCIETY OF AMERICA 
ridge of weathered granitic rock, east of which is the wide, deep channel of the 
Arroyo Seco, cut in the coarse, unconsolidated outwash material which forms the 
piedmont slope at the south base of the San Gabriel Mountains. East of this channel 
stands a relatively narrow fringe of residences and nondescript structures, before 
the busy center is reached. North, west, and south of the Laboratory is residential 
propei-ty and the grounds of the Annandale Golf Club. It is expected that the station 
will be reasonably free from traffic and town disturbances. 
Six seismometers have been put in operation at the Seismological Laboratory--  
three short-period, torsion-suspension, local-earthquake instruments (including 
the vertical-component) ; wo long-period, torsion-suspension, horizontal-component 
distant-earthquake instruments; and a compressed flat-spring vertical-component 
instrument of moderately long period which is under test in an early experimental 
stage. However, until better facilities for time-keeping and time-marking become 
available the operation of these instruments will not be on a good routine basis. 
Moreover, in addition to the absence of good time-keeping, instruments of this 
character equire considerable time for settling down and need repeated adjust- 
ments before they operate in a quite satisfactory way. This period has not wholly 
elapsed at this date of writing. 
During the year under report the instrumental and auxiliary equipment has 
been completed and installed, except for vertical-component seismometers, at the 
secondary stations at La Jolla, Santa Barbara, and Riverside. The instrumental 
equipment for a secondary station at the Observatory on Mount Wilson is now 
in an advanced stage of construction. 
The work of equipping the station at Riverside was begun in August 1926. 
Unforeseen needs developed and some time was required to supply them. The 
installation and preliminary adjustment were completed in October i926. Since 
then the station has been operating satisfactorily, except for time-keeping and time- 
marking. 
It may be remarked in passing that, utilizing the data of the station at Riverside 
in combination with the data of the instruments at Pasadena, we already have been 
able in one instance to locate the origins of one group of small shocks upon the so- 
called Whittier fault, in good agreement with macroseismic data reported verbally 
and in the press. The Whitt ier fault was not previously known to be active, though 
this had been strongly suspected. Notwithstanding this, it must be stated that the 
study of the Santa Barbara group of shocks, of the Imperial Valley group which 
occurred in January 1927, and, in fact, of .this Whittier fault group as well, makes 
it clear that for very precise location of shock-origins the formulas heretofore in 
use must be improved. It is too early to make a definite statement, but preliminary 
studies indicate that the hypothesis in regard to the structure of the earth crust 
advanced recently by Jeffreys is in closer accord with our recent instrumental find~ 
ings than the older hypotheses advanced by Wiechert and his students, and by A. 
Mohorovi~id and his son. 
Instruments were installed at the new secondary station at Santa Earbara during 
April 1927. This was done very soon after the electric wiring of the station was 
completed, making the station shelter available for use. This instrumental equip- 
ment has not yet settled down into good routine operation and there is no adequate 
arrangement for keeping and marking time at Santa Barbara. 
REPORT OF THE ADVISORY COMMITTEE 253 
The installation of instruments in the room provided for this purpose at The 
Scripps Institution of Oceanography at La Jolla was undertaken early in May 1927. 
The room set aside at La Jolla for seismometers was available in one sense much 
earlier than the beginning of our program of work, and piers designed for our use 
were constructed in it some time ago; however, owing to the size and shape of the 
room a relatively complex pier housing was required and experience had to be 
gained before this could be planned intelligently. As early as practicable this housing 
was designed and as soon.as it was completed and the electric wiring installed the 
instrumental pparatus was set up. This apparatus is not yet in good operation and 
adequate provision for the keeping and marking of time at La Jolla has not been 
made. 
Since the submission of our lastreport  he establishment of a secondary station 
on Mount Wilson, previously discussed, has been authorized and the shelter con- 
structed. As soon as the instrumental equipment can be completed the apparatus 
will be installed there. This station also will be defective for a time in respect o 
time-keeping and marking. 
As previously stated in these reports--the ideal method of marking time at the 
various stations of the network is to have all marked by the same identical clock 
by wire circuits, or, since this is impracticable on account of cost and not perfect in 
practical respects, by radio time signals sent out once a minute and received and 
marked automatically on the records at all places. To do this is a task of no small 
magnitude and it is not certain whether it can be done within permissible limits of 
cost. Nevertheless, it is pleasing to be able to report that considerable progress 
in this direction has been made during the year under report. This will be followed 
up vigorously in the ensuing months. If, however, this should fail, we have an 
alternative plan for very accurate time-keeping and time-marking, at less cost than 
usual for such service--timing to be checked at each station several times a day by 
radio time signals sent out from Annapolis, Mare Island, and other stations. 
Depending to some extent upon the solution (permanent or temporary) of the 
time-keeping and time-marking problem, it is expected confidently that the primary 
station at Pasadena nd the four secondary stations at Riverside, Santa Barbara, 
La Jolla, and Mount Wilson will be in satisfactory operation within a comparatively 
short time. 
Relatively brief experience with a very short period torsion-suspension vertical- 
component seismometer indicates that this is a fairly satisfactory instrument for 
the recording of local earthquakes which are not vanishingly feeble. 
Nevertheless the general problem of the vertical-component seismometer, with 
long or moderately long free period, bristles with difficulties. Several methods are 
still under consideration for the development of instruments with longer free 
periods, sensitive to the weak accelerations of teleseismic motion. Dr. J. A. Anderson 
and Dr. Sinclair Smith have experimented with a vacuum-suspension device, with a 
compressed flat-spring Suspension device (now being tested), and with a double- 
spring suspension device which will be tested later. A small vertical-component 
seismometer constructed at the Geophysical Laboratory under the direction of 
Dr. F. E. Wr ight  has been given careful table tests which show that it will require 
temperature control or temperature compensation to make it stable enough for 
practical use. 
254 BULLETIN OF THE SEISMOLOGICAL SOCIETY OF AMERICA 
After repeated attempts, a low-pressure capillary nitrogen glow lamp has been 
developed which operates with more than sufficient brilliancy with relatively low 
power consumption. It apparently has long life. If inexpensive means can now be 
found for producing and suitably controlling interruptions in current we will obtain 
thus one solution for a seismometer lamp which will write a line of intensely 
exposed ots, overlapping to form a continuous but not greatly overexposed line 
in ordinary running, but spaced apart at short intervals to indicate the course of 
large excursions in the case of strong disturbances of the seismometer. 
RECOMMENDATIONS 
It  is recommended that provision be made:  
1. For  further experimental  work on vert ical-component i struments 
for the stations already designated. 
2. For  the further study of minute-to-minute ime signals for simul- 
taneous record at all of the stations. 
3. For  further experimental  work in the study of cumulative stresses 
(t i lt  mechanism).  
4. For  two addit ional branch stations at appropr iate points to be 
selected. 
J. A. ANDERSON 
RALPH ARNOLD 
J. •. BUWALDA 
W. W.  CA1V2PBELL 
ARTHUR L. DAY (Chairman) 
A. C. LAWSON 
R. A. MILLIKAN 
HARRY FIELDING REID 
BAILEY WILLIS 
Advisory Committee in Seismology 


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