Abstract Strain seismograms of the Montana shallow earthquake of August 17, 1959 recorded at Isabella, California have the wave pattern predicted in 1904 by Lamb for a surface pressure pulse. This is equivalent to a dipole source such as given by the vertical bilateral fault slip which was observed at the surface. Similar recordings made at Ñaña of the deep Peruvian earthquakes of August 19 and 30, 1961, (Δ = 600 ± km, h = 600 ± km) have the pattern calculated by Pekeris for a buried vertical downward force in the form of a step in time. It thus appears that these shocks were generated by a sudden volume contraction at the focus which could be the result of a sudden change of state. Failure of conventional seismographs to record the patterns calculated by Lamb and by Pekeris is due to their low sensitivity to the very long period ground movement components involved, and their relatively high sensitivity to the short period components which are rendered oscillatory by the departure of the crustal characteristics from the homogeneous half space assumed in the theoretical computations.

The free oscillations of the earth have been experimentally verified from an analysis of strain seismograph and pendulum seismograph recordings made in California and Peru from the great Chilean earthquake of May 1960. Both spheroidal and torsional oscillations were revealed by a power spectral analysis of the seismograms. The gravest spheroidal mode shows a split spectral peak with periods of 54.7 and 53.1 minutes. The theoretical prediction for the Bullen B model according to Alterman, Perkeris, and Jarosch is 53.7 min. The oscillations were observed for all modes up to 38 with corresponding periods as short as 3.7 minutes. For the higher modes, agreement in the observed period is found between the Chilian earthquake and the Kamchatka earthquake of 1952. In almost all cases agreement between experimental and theoretical predictions is close. Differences which occur should make it possible to discriminate between the several earth models which have been proposed. From the width of the spectral peak, values of the dissipation function Q−1 for the earth could be determined with an accuracy greater than was previously possible. For the spheroidal mode S3(T = 35.5 min), Q = 380, and for the mode S18(T = 6.2 min), Q = 170. On the assumption that Q is independent of frequency, this implies a higher Q in the core than in the mantle. A method is described for deducing the fault length and rupture velocity from analysis of phase difference between components of ground motion. Preliminary results indicate a fault length for the Chilean earthquake of about 1000 km and rupture velocities in the range 3 to 4 km/sec.

THE effect of gravitational radiation on an elastic body has been previously investigated1. The component varying with time of the Riemann tensor (R iojo) associated with the gravitational field acts as a driving term in the wave equation for the strain or displacement. It was proposed1 that the normal modes of the Earth or a laboratory mass be used as a detector of gravitational radiation. Experiments to measure the interstellar gravitational radiation at kilocycle frequencies are at present in progress at the University of Maryland.

Phase and group velocities of mantle Love and Rayleigh waves obtained from strain seismograph records of the Chilean earthquake are presented. The velocities of mantle Rayleigh waves of period from 300 to 550 seconds agree with those predicted from periods of free spheroidal oscillation of the earth and do not show a flattening of the group velocity curve for periods greater than 380 seconds. Group velocities for mantle Rayleigh waves reach a maximum of 7.8 km/sec at a period of about 1000 sec. Study of initial phases of Rayleigh waves indicates a difference of phase of π between the azimuth to Isabella and the azimuths to Ñaña and Ogdensburg. Determinations of phase and group velocities of Love waves have been extended to periods of 700 seconds. The phase velocity data of Satô [1958] has been corrected for the polar phase shift. The correct curve has been identified from the numerous possible curves which result from a 2π ambiguity in the phase correlation made by Satô. Values of phase velocities are presented for periods in the range of 60 to 700 seconds. The group and phase velocities of both Love waves and Rayleigh waves agree well with those predicted for the Gutenberg-Bullen A model of the earth. It is verified that analysis of seismograms in terms of progressive wave trains is equivalent to analysis in terms of standing waves. In the presence of absorption, as for the earth, the analysis in terms of progressive wave trains has many advantages. Material supplementary to this article has been deposited with the ADI Auxiliary Publications Project, Photoduplication Service, Library of Congress, Washington 25, D.C. A copy may be secured by citing the document number 6816 and remitting $1.75 for 35-mm microfilm. Advance payment is required. Make check or money order payable to: Chief, Photoduplieation Service, Library of Congress.

ABSTRACT Descriptions and theories of a number of different seismographs developed particularly for recording of very long-period seismic waves are presented. These include (1) electromagnetic strain seismograph with galvanometer of 8 minutes period and photographic recording; (2) displacement transducer strain seismometer with resistance-capacitance network and short-period galvanometer photographic recorder or with ink-writing recorder; (3) electromagnetic pendulum seismometer with RC network having transfer characteristic of a long-period galvanometer recorder or a heated stylus visible writer; (4) electromagnetic pendulum with period increased tenfold or more using shunt capacitance; and (5) electromagnetic pendulum with condenser-lengthened period and triple RC integrating network recording with either heated stylus visible writer, ink writer, or short-period galvanometer photographic recorder.

Data are presented from a 5-year series of observations of geomagnetic fluctuations in the period range 0.3 to 120 seconds, approximately. These were carried on with flux rate variographs using pickup coils with 1-second-period galvanometers recording photographically at a trace speed of 1 mm/sec with maximum sensitivities of 0.05 gamma/sec per trace millimeter. Four characteristic types of oscillations are included in this study: Type A oscillations, approximately sinusoidal in form, range in period from 0.3 to 2.5 seconds and in southern California occur at night only. They exhibit a negative correlation with sunspot numbers. Type B oscillations are nearly sinusoidal in form with periods ranging from about 3 to 8 seconds. They appear to be associated with the local occurrence of auroras. Type C oscillations are nearly sinusoidal in shape with periods ranging from about 7 to 30 seconds. In southern California they occur in daylight and exhibit a strong correlation with sunspot numbers. Type D oscillations are transients in the form of single or multiple pulses or trains of several oscillations. The pulse breadths or oscillation periods range from about 40 to 120 seconds or more. They are strictly nocturnal in southern California with a sharp peak in the rate of occurrence at local midnight. Some characteristics of sudden-commencement components in the observed period range are mentioned briefly.

Research Article| August 01, 1959 FUSED-QUARTZ EXTENSOMETER FOR SECULAR, TIDAL, AND SEISMIC STRAINS HUGO BENIOFF HUGO BENIOFF SEISMOLOGICAL LABORATORY, CALIFORNIA INSTITUTE OF TECHNOLOGY, 220 N. SAN RAFAEL AVE., PASADENA, CALIF. Search for other works by this author on: GSW Google Scholar Author and Article Information HUGO BENIOFF SEISMOLOGICAL LABORATORY, CALIFORNIA INSTITUTE OF TECHNOLOGY, 220 N. SAN RAFAEL AVE., PASADENA, CALIF. Publisher: Geological Society of America Received: 18 Aug 1958 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1959, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1959) 70 (8): 1019–1032. https://doi.org/10.1130/0016-7606(1959)70[1019:FEFSTA]2.0.CO;2 Article history Received: 18 Aug 1958 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation HUGO BENIOFF; FUSED-QUARTZ EXTENSOMETER FOR SECULAR, TIDAL, AND SEISMIC STRAINS. GSA Bulletin 1959;; 70 (8): 1019–1032. doi: https://doi.org/10.1130/0016-7606(1959)70[1019:FEFSTA]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract A description is given of two fused-quartz extensometers located in mountain tunnels at Dalton Canyon and Isabella in Southern California and designed for observing long-period seismic-wave strains, earth tidal strains, and secular strains. They consist essentially of instruments for measuring and recording variations in the separation of two piers by comparison with a length standard of fused-quartz tubing. The sensitivity for secular strains, denned as the least detectable strain increment, is approximately 10−7. For tidal and seismic-wave strains, the sensitivity is higher—a 1-mm deflection of the recorder represents a strain increment of 5.2 × 10−10. In both cases the maximum usable sensitivity is limited by ground-strain unrest or noise, generated by wind, barometric-pressure variations, temperature variations of the surface layers of the ground, and variations in ground-water saturation. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

On July 1, 1957 Beno Gutenberg retired as Director of the Seismological Laboratory and was succeeded by Frank Press. Beno Gutenberg remains a member of the staff. On February 5, 1958, Harry 0. Wood, who founded the Seismological Laboratory, passed away after a long illness. The long‐standing condition of overcrowding it the Seismological Laboratory was corrected by the acquisition of an adjacent property. The new quarters, known as the Donnelley Laboratory, house offices for staff, visitors, and students as well as a library, map room, seismogram analysis room, and ultrasonic seismic model laboratory. An important feature of the Donnelley Laboratory is a tunnel 150 ft long, located in granite at a depth of 60 ft beneath the building. A linear strain seismograph and ultra long‐period pendulums will be installed in the tunnel. The old quarters are being extensively remodeled and will be known as the Kresge Laboratory, housing the main seismograph vaults and recording rooms, experimental piers, electronics laboratory, machine shop, storage and stock rooms, photographic dark room, and offices for technicians.

The responses of conventional seismographs are such that earthquake waves in the period range of about 5 to 20 seconds are written with such large amplitudes an the seismograms that longer period waves cannot be observed. Consequently, in order to increase the observable range to substantially longer periods, I developed an electromagnetic strain seismograph having a recording galvanometer of three minutes period and an equivalent pendulum magnification factor for surface waves of 20. The first great earthquake which has occurred since this seismograph combination was put into service was the Kamchatka shock of 1952, November 4. Studies of the aftershock sequence of this earthquake have indicated that in the principle shock faulting extended approximately 1,000 km with an average slip of about 15 feet. Figure 1 shows a portion of the seismogram of this earthquake written with the new instrument. The most prominent event on this record is the G1 wavelet, which is a horizontally polarized surface wave with no vertical component. Although the G wavelet is a Love wave, its frequency components · all lie in that part of the dispersion curve which is essentially flat, and, consequently, the wavelet propagates without substantial change of shape. Thus, although the duration of G2 which has traveled over the longer arc has been increased to 180 seconds owing to differentially greater absorption of the higher frequencies, its shape is not changed. The apparent change in shape is a result of the instrument response characteristics. The response to the 60-second pulse of G1 is proportional to ground particle displacement, since the pulse frequency components are mainly greater than the galvanometer frequency. With G2, the frequencies cluster about the frequency of the galvanometer, and the over-all response is thus approximately proportional to the ground particle velocity. The G2 pulse as written on the seismogram is thus the first time derivative of the G1 pulse, indicating identity of shape for the two. The time of travel for a complete circuit around the earth for the G wave was measured on the seismogram by comparing the arrival time intervals of G4–G2 and G3–G1 . It is 152.3 minute This corresponds to a surface velocity of 4.38 km per second, which is lower than the value to be expected for a shear wave which penetrates as deeply as the G wave. Figure 2 is a portion of the seismogram containing G1 and R1.

Summary Long period seismograph systems in operation in Pasadena are described. Extension of the group velocity curves for mantle Rayleigh waves and G-waves, the detection of these waves from earthquakes in the magnitude range , and the recording of unusual body waves with unsuspected long period components are among the results which have been achieved.

Abstract Aftershock epicenters of the Kamchatka earthquake of November 4, 1952, are distributed over an area approximately 1,030 kilometers in length by 240 kilometers in width. Assuming that this distribution represents the active strain zone, the total average strain, average elastic energy, and average stress of the rocks before slip were 11.9 × 10−5, 1.35 × 102 ergs/cm.3, and 12.6 kg/cm.2, respectively. The strain-release curve of the sequence has been constructed using observations from Uppsala and Kiruna. The data include more than 400 shocks with magnitudes 6.0 and greater which have occurred up to December, 1956. The curve exhibits three segments each of the form ΣJ1/2 = A + B log t, where J is the energy and t is the time measured from the time of the principal earthquake. The slope B changes abruptly at t = 0.4 days and at t = 195 days, the latter change being particularly pronounced. Moreover, this was accompanied by other evidence suggesting a change in mechanism. The coefficients B have almost the exact ratio of 1 : 2 : 5 in the three intervals 0-0.4, 0.4—195, and after 195 days. The aftershock activity has its highest concentration in the vicinity of the principal earthquake and tapers off toward both ends of the active fault segment. The majority of the aftershocks have clear pP impulses occurring generally 9 to 13 sec. after P, indicating that the foci were in or close to the Mohorovičić discontinuity. The rate of strain accumulation and release for the time interval from 1897 to 1956 for the entire Kamchatka-northern Japan stress system shows a slow decrease with time. Comparison of the rate of the entire system with that of the aftershock sequence leads to an approximate estimate of the possible duration of the sequence.

Palos Verdes: 33° 45.5′ N, 118° 21.4′ W, h = 340 meters, short‐ and long‐period Benioff vertical. Installed March 21, 1956. Hayfield: (Hayheld pumping station, Metropolitan Water District) 33° 42.4′ N, 115° 38.2′ W, h = 440 m; temporary equipment: short‐period BeniofT horizontal, which has recorded an unexpectedly large number of shocks at short distances. Installed June 20, 1956.

Automatic‐calibration weight lifters for daily checking of amplitude response and phase have been attached to Benioff reluctance instruments at Pasadena, Tinemaha, and Isabella. Red safe lights of an improved type have been installed at most of the stations; these allow the use of a lighter and less expensive grade of recording paper. The vertical‐component recorder at Dalton has been transferred from film to the new paper. Three small house trailers are being outfitted as portable stations. Two portable seismographs using vertical and horizontal pendulums and variable discriminator transducers have been set up to record by the hot‐stylus method, and are maintained in reserve for emergencies. Several additional film‐recording units can be put into the field on short notice.