EARTHQUAKES.

Press, Volume LXI, Issue 18461, 15 August 1925, Page 14

EARTHQUAKES.

LOCALISING SOURCES OF CREEPS. • i RESEARCH IN CALIFORNIA. Dr. Arthur L. Day, of tlio Geo physical Laboratory, reports for llio several organisations working on California earth, movements in "Science," March 27th, 1925. The object is to focus scient'ifio measurements on the inside of mountain ranges and sea-bot-tom, so as to localise, not only the sources of earthquakes, but the centres of mountain building and creep of surface ground. To this end the Carnegie Institution, the California Universities, the U.S. Geological Survey, the Navy, and tho U.S. Coast and Geodetio' Survey arc co-operating. Tho Advisory Committee on Seismology is aided' i>y both the Geophysical Laboratory of Washington and the shops and laboratories of the Mount Wilson Observatory at Pasndena. 1 The committee was appointed in 1921. _ Lawson had concluded from jnriation-of-latitude observations that tho earth's crust near San Francisco had been drifting north a foot a year for 20 years. Lambert showed that probable errors were of the same order of magnitude as the assumptions indicating creep, so "that Lawson's co"nclusvon was not final. Thei'e are lateral displacements of 20 feet in places along tho great fault that moved during the earthquake of_ 1906. A new base line for trunigulation of tho whole region was adopted recently iu the Sierra rvcvndas, and work for sevcYal years including 1925, supplemented by levelling! showsthat a prior base line nearer San 1' rancisco has itself moved southward some five feet. Another region tcr tho south and some distance from tho fault slip has moved north 24 feet. Messrs Ts oblo and Kew have located nev active faults in southern California. The Hydrographio Offioe of the JNavy with 6onic souuding apparatus, assisted by tho Coast Survey, is desloping new -mans of the sea-bottom off Can form a. For determining loral earthquakes, tremors and tiltincs, J. A Anderson and H. 0. Wood have mado new instruments in Pasadena; these are being tested, improved, and manufactured, and seismographs on a new principle are actuallv working at magnifications of from 1200 to 4000. Other devices are beiner experimented with to solve* the problem of uniform tiros service at separated stations. A number of California and Arizona stations have been selected for work on local motion. Eventim'ly tho Coast Survey hopes to standardise and improve registration of distant large earthquakes, at such stations as Hawaii, Alaska, Arizona, Washington, and Porto Rico. Dr. Day mentions in ins report the interesting possibility of instrumental measurement continuously of deep-seated rock pressures underground, through some such instrument as a metal bulb containing a fluid connected by a tubo with the surface, the bulb bein<* cemented in a deep subterranean chamber. i If tilt and creep and changes of level can be precisely measured. Dr. Day thinks that in any given place known to be moving, the site of the next sudden release may be reasonably determined in advance. Prediction of the time of rupture is much more difficult.