Strong Motion Accelerographs Research Articles

Strategies for strong motion earthquake recording in New Zealand

The problem of how to record future strong earthquakes in New Zealand is examined by considering what data is required, how effective the present network will be in gathering that data, and what new technology is now available. It is concluded that present methods result in an unsatisfactory use of funds. There is a current emphasis on frequent expert servicing which, while it leads to a high probability of any recorder operating, restricts the number of installations able to be serviced. Thus we have a high probability of any given recorder working, coupled with a small probability of any given earthquake being within range of a recorder. The suggested future strategy is to first develop a new accelerograph of high reliability and the capability of self testing. This would incorporate a non volatile no moving parts electronic memory. Servicing of this would be at infrequent intervals, but a program of reporting the self test results by postcard would be adopted. By thus cutting down on recorder servicing and record processing times, we could force the major factor to be capital cost, and thus allow the network to expand until a realistic probability of recording a major earthquake was reached. The installation of about 70 additional strong motion accelerographs in the main seismic region would allow a good chance of recording our next major earthquake.

Algorithm development for signal-selective seismic field recorders

A seismic field recorder has been developed based on the MC6800 microprocessor [W.M. Adams, Geophys. Prospect. (to be published, 1977)]. This allows the real-time implementation of algorithms for selecting the signals from the microseismic background and hence for recording primarily signals. The advantages are the greatly reduced amount of recording media that must be processed at the central data-processing depot and the reduction in the amount of data processing that must be done later; the current disadvantages are the battery requirements, the complexity of the equipment, and the lack of effective algorithms. The first two defects will be solved by component evolution; here we discuss the last factor. The present system is not self-adapting. Instead, continuously recorded data are processed by heuristic procedures to find an improved method of selecting the signals from the background. Because of spurious impulsive noise, an energy-content discriminator followed by a zero-crossing (frequency) discriminator is found to be superior to the usual threshold trigger, such as used to turn on the strong motion accelerographs for earthquake engineering research. The algorithm used by the Seismic Research Observatory (SRO) of the USGS is compared with the energy-content + zero-crossing processing. [Work supported by NSF.]

Characteristics of electromagnetic starters for strong motion accelerographs

Letter| December 01, 1977 Characteristics of electromagnetic starters for strong motion accelerographs W. J. Rihn; W. J. Rihn Kinemetrics, Inc.222 Vista Avenue Pasadena, California 91107 Search for other works by this author on: GSW Google Scholar W. J. Beckmann W. J. Beckmann Kinemetrics, Inc.222 Vista Avenue Pasadena, California 91107 Search for other works by this author on: GSW Google Scholar Bulletin of the Seismological Society of America (1977) 67 (6): 1667–1669. https://doi.org/10.1785/BSSA0670061667 Article history received: 07 Oct 1976 first online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Tools Icon Tools Get Permissions Search Site Citation W. J. Rihn, W. J. Beckmann; Characteristics of electromagnetic starters for strong motion accelerographs. Bulletin of the Seismological Society of America 1977;; 67 (6): 1667–1669. doi: https://doi.org/10.1785/BSSA0670061667 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search nav search search input Search input auto suggest search filter All ContentBy SocietyBulletin of the Seismological Society of America Search Advanced Search This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not currently have access to this article.

Strong motion seismology

Strong motion accelerographs and data processing systems for the measurement of strong ground motion of damaging earthquakes are described with some comments on future developments. Some information is given on the earthquakes and instrumentation sites for which important records have been obtained. Studies of the areal distribution of ground motions during earthquakes are discussed in terms of transmission path effects. Some speculations are advanced concerning the establishment of limiting values of earthquake ground motions.

Strong-motion earthquake accelerograms at Brawley, California: January 25, 1975

abstract During the Brawley earthquake swarm of January–February, 1975, a single strong-motion accelerograph installed after the swarm began recorded 27 positively identified earthquakes in 14 hr, at hypocentral distances of approximately 5 km. Eight of these had magnitudes (ML) ≧ 3.5, and several had ML < 2.5; the instrument independently triggered 18 times. Peak accelerations in excess of 10 per cent g were obtained for five of the eight earthquakes with ML ≧ 3.5, and a peak acceleration of 25 per cent g was recorded for the largest event, ML = 4.3.

やや長周期の微動観測と地震工学への適用 (2)

This is a continuation of the research on the observation of long-period microtremors for elucidating ground characteristics during an earthquake. Results of observation along a line of about 17km from Hachinohe to Misawa cities in Aomori Prefecture, Japan, are outlined in this paper. Essential efforts were made on the affirmation and extension of the conclusions in the previous paper—a systematic change of predominant periods of microtremors along a 5km-line from 0.7sec at the point close to the outcrop of the bed rock to 2.5sec at the strong motion accelerograph site, and the relation of the predominant periods to the deeper underground conditions. Instruments, observations, and data processings are almost the same to those in the first paper.The results obtained are as follows. First, the reobservation of the microtremors along the same line revealed a similar and very systematic change of the predominant periods, though the spectrum of the input motions to the ground layers seemed significantly diferent. Second, the observation extended as far as Misawa city brought the longest predominant period of 3.5sec at the end point, and produced the conclusion that the changes of the period of microtremors were very responsible to the undulation of the bed rock formation. The layer thickness corresponding to 3.5sec in period was estimated as about 500m.This investigation strongly suggests the importance of knowing the ground dynamic characteristics down to 500-1000m in depth for the aseismic construction of large-scale structures and thus the significance of observation of the long-period microtremors.

Seismic Instrumentation of Dams

The desirability of installing seismic instruments on and near major dams is explained. Two types of instruments are required: (1) Strong-motion accelerographs for recording potentially destructive ground shaking and resulting dam vibrations; and (2) sensitive seismographs for determining the local seismicity. A minimum of two strong-motion accelerographs should be installed on the dam and a minimum of two should be installed in the immediate vicinity of the dam. Each accelerograph should record three components of motion, should have a natural frequency of approx. 20 Hz, a recording speed of approx 1 cm/s. The sensitive seismographs are intended to record the local seismicity in the vicinity of the dam site before construction, and to detect any changes in seismicity during reservoir filling. A minimum of three seismographs is recommended for installation in the vicinity of the dam site. A vertical-component seismometer (1 Hz - 5 Hz) with visual recorder and approx l0,000 magnification at 1 Hz is recommended.

A note on the nonlinear response of the pendulous accelerometer

abstract When the pendulous accelerometer experiences large off-axis acceleration in a direction which produces significant along-the-boom acceleration, the dynamics of the instrument are altered and it becomes nonlinear in its response. The response to an off-axis horizontal acceleration step is derived and found to exhibit small changes in damping, overshoot, damped resonant frequency, and final value of boom position. The size of these effects is negligible for all but the largest accelerations and even then acceptable. The change in overshoot is the largest, about 5 per cent, for an AR-240 strong-motion accelerograph subjected to a 1-g horizontal acceleration step at 45° to the sensitive axis. An expression is developed for the steady-state response to off-axis sinusoidal acceleration. In addition to the proper response, it contains both a double frequency term and a constant offset. The size of these terms is discussed and an example is given.

Spatial and temporal variations ints/tpand inPwave residuals at Blue Mountain Lake, New York: Application to earthquake prediction

Renewed earthquake activity at Blue Mountain Lake (BML), New York, in July 1973 provided an excellent opportunity to monitor the travel time ratio of S to P waves (ts/tp) in real time and to test the ts/tp technique as a predictive tool. From a mean value of 1.73 on July 30, 1973, ts/tp decreased to about 1.5 over the next 2–3 days. On August 1 a prediction was made that an earthquake of magnitude 2.5–3 would occur in a few days. Upper limits of the magnitude and the time of occurrence of the expected earthquake were inferred from the spatial extent of the seismic anomaly. As a result of the prediction an additional strong motion accelerograph (SMA) was installed in the source region. At 2310 UT on August 3,1973, a magnitude 2.6 earthquake occurred at BML and triggered two SMA's. In addition to the seismic activity a number of explosions were recorded from a variety of azimuths. The P wave arrivals from distant quarry blasts, refracted from a high-velocity layer at 4 km beneath BML, showed late arrivals at five stations during the premonitory low in ts/tp. The P wave delays were maximum (0.13 s) in the hypocentral region of the earthquake and decreased away from it along two profiles. These results indicate that changes in ts/tp are caused by changes in the material properties of the earthquake source region. The anomalous zone (region of low P velocity) for the August 3 earthquake (aftershock length 1 km, depth 1±0.1 km) was about 3–5 km in radius and was wholly or largely limited to the layer above the interface at 4-km depth. In contrast to the P delays observed from distant quarry blasts, P and S arrivals from local construction blasts (Δ < 10 km) show no large premonitory changes in either P or S travel times. This observation suggests that either no significant velocity anomalies occurred in the upper 0.5 km of the BML region or that the dilatant cracks were predominantly horizontal, the result being strong velocity anisotropy. This conclusion is supported by data from seismic sources; events located at shallow depths show normal (1.75) to high (1.85) ts/tp values even when values as low as 1.5 are observed from deeper sources. This finding places constraints on the use of artificial sources to monitor changes in velocity, since the effects of anisotropy may have to be taken into account in addition to ensuring that ray paths to the recording stations penetrate the zone of anomalous velocity. A maximum likelihood method was used to invert data from individual small earthquakes to determine P and S velocities in the anomalous zone. The results, which are consistent with the explosion data, indicate that the premonitory decreases in P and S velocities were much more pronounced for sources at depths of 1–2 km than for those near the surface. The inferred low values of P and S velocities were, respectively, about 22 and 12% below normal. This study also shows that ts/tp inferred from a Wadati plot is a function of the distribution of stations relative to the anomalous zone. To optimize the use of ts/tp as a predictive tool, this study suggests that not only temporal but spatial variations of velocity anomalies should be monitored. This emphasizes the need for multistation coverage for reliable earthquake prediction.

An array of strong-motion accelerographs in Bear Valley, California

Fifteen strong-motion accelerographs, each with the capability of writing the WWVB absolute time code on the recorded accelerogram, have been deployed in an elliptical array, at a station spacing of several kilometers, along the San Andreas Fault in the Bear Valley region of central California. Ten accelerograms were obtained for the June 22, 1973, earthquake (M = 3.9), located near the center of the array. Preliminary analyses of these accelerograms support previous suggestions that the crystalline rocks of the Gabilan Range possess higher material velocities and lower intrinsic absorption than do the Cretaceous and Cenozoic sedimentary rocks northeast of the fault zone. These accelerograms clearly indicate that a strong-motion accelerograph array of this sort can provide the basic data for source mechanism, wave propagation, and local ground-motion studies for earthquakes with magnitudes as small as 3.5-4.0.

On the correlation of seismic intensity scales with the peaks of recorded strong ground motion

Correlations of the recorded peak acceleration, velocity and displacement, and the Modified Mercalli intensity have been carried out for 57 earthquakes and 187 strong-motion accelerograms recorded in the Western United States. Correlations of peak acceleration with intensity, characterized by the data scatter exceeding one order of magnitude, have lead to average peak accelerations which are higher than those reported by a majority of previous investigators. New correlations, also characterized by scatter of data of about one order of magnitude, have been presented for peak velocities and displacements of strong ground motion versus Modified Mercalli intensity. Grouping of all recorded data according to the geology underlying the strong-motion accelerograph stations was carried out and permitted a study of the possible effects that local geology might have on the peaks of strong-motion acceleration, velocity, and displacement. Results of this analysis are as follows: (1) For ground shaking of a particular Modified Mercalli intensity, average peak acceleration recorded on hard rock is higher by a factor less than about two than the average peak acceleration recorded on alluvium; (2) the effect of local geology on the average peak velocity leads to marginally higher peak values on alluvium; and (3) the peak ground displacements are larger, by a factor less than two, when recorded on alluvium rather than on hard rock.

First strong-motion records from a central or eastern United States earthquake

Two strong-motion accelerographs were installed at Blue Mountain Lake, New York (BML) shortly after the initiation of a swarm-type sequence of earthquakes in mid-July of 1973. Three records rich in frequencies as high as 35 Hz were obtained from two of the largest events (magnitude 2.7 and 2.6), the foci of which were between 1.0 and 4 km from the accelerograph stations. The maximum acceleration recorded was −0.034 g at 25 Hz. These are the first strong-motion records obtained from east of the Rocky Mountains. Inasmuch as strong-motion results from the Western United States may not be applicable to the eastern two-thirds of the United States, these new results have important implications for the design of critical facilities such as nuclear power plants, liquified gas storage tanks, and large dams.

Earthquake instrumentation for nuclear facilities

Regulatory and industry guidelines have been developed in the US for earthquake instrumentation so that factual site and structural response records will be made during earthquakes. These guides have resulted in the development of specialized sensor, recorder and display units which can meet the functional and environmental specifications. Prompt operator access to the recorded data is important, so that both unsafe continued plant operation and unwarranted shutdown can be avoided. The strong motion accelerograph is the basic and principal instrument for this application. This system records acceleration time histories of response for remotely located triaxial sensor units. Additional instrumentation including peak recording accelerographs and response spectrum recorders are used to augment the basic system. Detailed analyses will be carried out after a significant earthquake using mathematical models and the recorded structural response data. The validity of the models must be verified before confidence can be placed in the calculated results. Experimental testing techniques for the full-scale structure which are useful in the model validation process are described.

Parkfield, California, earthquake of June 27, 1966: A three-dimensional moving dislocation

abstract Recordings from five strong-motion accelerograph stations have been used to derive a three-dimensional dislocation model for the Parkfield Earthquake. The model consists of a buried fault which extends from a depth of 3 km to a depth of 9 km below the ground surface. It appears from the analysis, which considers various fault lengths, that the zone of significant faulting was the 20-km-long northwestern section of the fault. The rupture velocity has been found to be between 2.4 and 2.5 km/sec and the dislocation amplitudes have been found to be about 120 cm. There have been comparisons made of the model results with geodetic data on static deformations and creep measurements following the event. In contrast with several other source mechanism studies of the Parkfield event, this model yields a picture which appears to be very consistent with both the dynamic strong-motion measurements as well as the available geodetic and creep data.

A three-dimensional dislocation model for the San Fernando, California, earthquake of February 9, 1971

The data from five strong-motion accelerograph stations centered above and surrounding the fault are used to develop an approximate three-dimensional dislocation model for the San Fernando earthquake. In the resulting model, the dislocation originates near the instrumentally determined epicenter at a depth of 9.2 km and then propagates southward and upward with a velocity of 2 km/sec. Calculated dislocation amplitudes of about 10 m in the hypocentral region have been found to decay to about 1 m toward the center of the fault and then build up again to about 6 m just before the fault intersects the ground surface in the San Fernando Valley. The assumed fault area of 130 km^2 and the assumed rigidity µ = 3 × 10^(11) dyne/cm^2 give a moment M_0 = 1.53 × 10^(26) dyne-cm. This study indicates that, with several strong-motion accelerographs suitably located in the epicentral region, it is possible to find a kinematic faulting process associated with the periods of ground motion which are longer than about 1 sec.

The calculation of horizontal accelerations from seismoscope records

abstract The seismoscope is a simple instrument designed originally to give a largely qualitative indication of the strong ground motions produced by an earthquake. It consists of a smoked watch glass attached to a two-degree-of-freedom pendulum with a period of 34 sec and damping about 10 per cent of critical; a pen records the pendulum motions on the watch glass. One point on the displacement spectrum of the recorded ground motion at this period and damping is obtained from the measurement of the maximum pendulum excursion. An examination of the seismoscope record obtained on the east abutment of the failed Lower San Fernando dam during the 1971 San Fernando earthquake showed a high-frequency vibration superimposed on the general oscillations. It did not seem likely that this was solely an earthquake vibration component, and shaking table tests of seismoscopes revealed the presence of a seismoscope vibration mode at frequencies of 15 to 18 Hz depending on the instrument. The oscillations due to this mode on the abutment seismocope record have, therefore, been used as timing marks, to enable the seismoscope equation to be solved for the input acceleration components. The results of the calculations are presented along with analyses of the seismoscope response to indicate the range of applicability. One other record, obtained on a seismoscope alongside a strong-motion accelerograph, was also analyzed for comparison with the recorded accelerations, to demonstrate the validity of the technique. The timing vibration appears on a number of seismoscope records.

Strong Motion Accelerograph Records From Sep., 4, 1972 Stone Canyon Earthquake

A magnitude 4.7 (BRK) earthquake on 4 September 1972 in the area of the NOAA Stone Canyon Geophysical Observatory produced a strong-motion accelerograph recording of 0.7 g acceleration, the second highest known recorded acceleration.

Strong motion earthquake recording in New Zealand

An extensive network of strong-motion accelerographs is installed on the ground throughout New Zealand and also in major structures. At present this system contains 77 three-component recorders and 74 two-component non-timebase recorders. Since severe earthquakes are rare, and their violence may be very different at nearby positions, the strong-motion earthquake records must be supplemented by seismological, geological and geophysical data in order to obtain adequate information for the design of earthquake-resistant structures.

Analysis of the Station No. 2 seismoscope record—1966, Parkfield, California, earthquake

Abstract During the 1966 Parkfield, California, earthquake a strong motion accelerograph and an adjacent seismoscope were located essentially at the causative fault. The accelerograph component parallel to the fault malfunctioned and left no recorded trace. The seismoscope record and the component of the ground motion perpendicular to the fault are used to reconstruct the acceleration component in the direction parallel to the fault. The details of the derived acceleration parallel to the fault differ from the past recorded strong ground motions in that higher frequency components are present. The peak ground accelerations transverse and along the fault are found to be of the same order of magnitude.

Soil-structure Interaction At TheEl Centro Terminal Substation

The objective of this paper is to report on possible soil-structure effects that may have affected previously recorded earthquake motions at the instrument site housed in the Terminal Substation Building in El Centro, California. This site was selected for this study as more strong motions accelerograms have been recorded at this site than at any other site in the United States. The soil-structure effects were analyzed using the pseudo three-dimensional plane strain finite element program FLUSH. The comparison of recorded and computed motions revealed the existence of interaction effects that may be attributed to the underlying soft soils and the very stiff structure of the El Centro Terminal Substation Building. These effects are strong at high frequencies (i.e. from 8 to 10 Hertz). As expected, it was also observed that at the higher frequencies and accelerations, soil nonlinearity had a significant influence on the recorded motions. INTRODUCTION During an earthquake, the ground shaking is typically recorded by a strong motion accelerograph. Such records may be made at locations in the free field (i.e. away from nearby structures) or within buildings. Typically, the recording made within a building will be influenced by the inertial forces generated by the structure. However, the nature and magnitude of this soil-structure influence has only been investigated recently (Crouse et al. [1]; Luco et al. [2]; Moudud [3]). This study reports on the possible soil-structure interaction effects that may have influenced motions recorded within the Terminal Substation Building in El Centro, California. This accelerograph station has contributed more records to the current library of strong motion data than any other station in the western United States. Thus it would be relevant and pertinent that the influence of SSI effects be examined for this site. Transactions on the Built Environment vol 3, © 1993 WIT Press, www.witpress.com, ISSN 1743-3509 582 Soil Dynamics and Earthquake Engineering