Seismometer System Research Articles

MarsQuakeNet: A More Complete Marsquake Catalog Obtained by Deep Learning Techniques

AbstractNASA's Interior Exploration using Seismic Investigations, Geodesy and Heat Transport (InSight) seismometer has been recording Martian seismicity since early 2019, and to date, over 1,300 marsquakes have been cataloged by the Marsquake Service (MQS). Due to typically low signal‐to‐noise ratios (SNR) of marsquakes, their detection and analysis remain challenging: while event amplitudes are relatively low, the background noise has large diurnal and seasonal variations and contains various signals originating from the interactions of the local atmosphere with the lander and seismometer system. Since noise can resemble marsquakes in a number of ways, the use of conventional detection methods for catalog curation is limited. Instead, MQS finds events through manual data inspection. Here, we present MarsQuakeNet (MQNet), a deep convolutional neural network for the detection of marsquakes and the removal of noise contamination. Based on three‐component seismic data, MQNet predicts segmentation masks that identify and separate event and noise energy in time‐frequency domain. As the number of cataloged MQS events is small, we combine synthetic event waveforms with recorded noise to generate a training data set. We apply MQNet to the entire continuous 20 samples‐per‐second waveform data set available to date (>1,000 Martian days), for automatic event detection and for retrieving denoised amplitudes. The algorithm reproduces all high quality, as well as majority of low quality events in the manual, carefully curated MQS catalog. Furthermore, MQNet detects ∼60% additional events that were previously unknown with mostly low SNR, that are verified in manual review. Our analysis on the event rate confirms seasonal trends and shows a substantial increase in the second Martian year.

A Half-Year Long Observation at Sakurajima Volcano, Japan Using a Multi-Channeled Seismometer System with Phase-Shifted Optical Interferometry

The performance of a multi-channel seismometer system with phase-shifted optical interferometry was improved by newly introduced sensors and a processing unit. The current version of the system consists of three optical wired seismometers and the unit. We deployed the system at Sakurajima Volcano and successfully operated it from June to December 2019. As the Sakurajima Volcano frequently erupts, a number of eruption events were observed during the observation period, as were a number of lightning strikes. In this study, we evaluated the observation performance of the volcanic earthquake and the noise caused by the lightning, using the spectrum and amplitude of the waveform. The results show that this sensor can observe earthquakes caused by eruptions as well as ordinary seismometers do. When the lightning struck, pulsed noise with power in a wide frequency band was observed in the existing seismometer, but not in the new sensor. Therefore, the observation was not affected by lightning. In addition, this system was found to be effective in the array analysis of volcanic earthquakes.

Marine Sediment Characterized by Ocean‐Bottom Fiber‐Optic Seismology

AbstractThe Sanriku ocean‐bottom seismometer system uses an optical fiber cable to guarantee real‐time observations at the seafloor. A dark fiber connected to a Distributed Acoustic Sensing (DAS) interrogator converted the cable in an array of 19,000 seismic sensors. We use these measurements to constrain the velocity structure under a section of the cable. Our analysis relies on 24 hr of ambient seismic field recordings. We obtain a high‐resolution 2‐D shear‐wave velocity profile by inverting multimode dispersion curves extracted from frequency‐wave number analysis. We also produce a reflection image from autocorrelations of ambient seismic field, highlighting strong impedance contrasts at the interface between the sedimentary layers and the basement. In addition, earthquake wavefield analysis and modeling help to further constrain the sediment properties under the cable. Our results show for the first time that ocean‐bottom DAS can produce detailed images of the subsurface, opening new opportunities for cost‐effective ocean‐bottom imaging in the future.

Seismic Observation and Analysis Based on Three-Component Fiber Optic Seismometer

We demonstrate a three-component fiber optic seismometer for seismic observation, with no electronics in the sensor probe, but relying exclusively on optical fiber in the form of an unbalanced Michelson interferometer, with state-of-the-art performance characteristics. The fiber optic seismometer system is installed in the seismic observation cave at the Earthquake Administration Bureau of Jilin Province, in Changchun, Jilin, China, and has been operating without interruption for more than a year. Two minor earthquakes of different magnitudes recorded by the three-component fiber optic seismometer are analyzed and discussed in detail from the perspectives of time domain and frequency domain signal quality and fidelity. In addition, the recording results of the fiber optic seismometer are compared with those of the traditional electrical-mechanical seismometer co-located at the observation site. Actual observational results of the seismic events show that the three-component fiber optic seismometer can record the seismic waves clearly, with comparable performance as the conventional seismometer.

Feasibility Study on a Multi-Channeled Seismometer System with Phase-Shifted Optical Interferometry for Volcanological Observations

A new Phase-Shifted Optical Interferometry seismometer system was tested in terms of its feasibility for multi-channeled volcanological observations in two volcanos in Japan. The system is capable of both sensing ground motions and transferring its signals through optical means. The prototype of this system comprises three optical-wired stations and optical components, and was deployed in Sakurajima Volcano in 2016 and in Asama Volcano in 2017. The system successfully operated for 134 days in total and provided seismograms that are in good agreement with those obtained using conventional systems. Several obstacles for putting this system to practical use that need to be solved were found through tests. Their solutions will be explored in subsequent research.

Determining the Natural Frequencies of the Dam at the Sayano-Shushenskaya Hydroelectric Power Plant Based on Data from a Seismometer System and Computations

A method for measuring the natural frequencies of the arch-gravity dam at the Sayano-Shushenskaya Hydroelectric Power Plant based on data from a seismometric network is described. Experimental and computational determinations of the natural frequencies are compared. It is shown that the calculated values are more sensitive to changes in the upstream water level than the values derived from the field measurements.

Three-Point Electromagnetic Spider Web

Simple three-point electromagnetic spider web combined with the host and the 30 m, 300 m, 3000 m 3 transmitters and 3 receiver circuits, telluric electricity and magnetic switch. Here the space electric field change by using the designed solenoid spider does not need deep inside the earth, and a seismometer and earthquake prediction control system is simple. After years of testing, with the use of every minute it is four times 5-10 second detection magnetic anomaly, and abnormal situation will be asked after the three behind the road before the earthquake electromagnetic parameters are converted to a digital signal electric parameter. If finding electromagnetic anomaly in 30 square kilometers will start the GSM switch remote alarm, using Maxwell’s equations theory and practice the test showed that this method can not only be used for electromagnetic anomaly before the earthquake prediction, and a plurality of electromagnetic webs can determine epicenter group composition. Before the earthquake changes in the electromagnetic field in a few hours to a few days, we are able to know in time that an earthquake is about to occur, and determine the location of the epicenter. The devices may be detected over stealth aircraft [1] [2] [3].

A seismic refraction survey conducted for the Ocean Bottom Cabled Seismometer system installed in the Japan Sea

A seismic refraction survey conducted for the Ocean Bottom Cabled Seismometer system installed in the Japan Sea

Development of Seismometers Sensor Network for Observation on Sea Floor ——P goes to Oceans——

Because large earthquakes have repeatedly occurred in subduction zones, it is important to observe seismic activities on the sea floor. An ocean bottom cabled seismometers (OBCS) system is the most suitable tool for this purpose since data can be obtained in real-time. Although the existing OBCS systems are useful for the study of seismic activities, the number of stations is limited due to their cost. Therefore, lower cost in both production and installation is desired. We have developed a new OBCS system utilizing IP technologies. IP technologies yield the new OBCS system that are more compact and less expensive, while a large amount of complex hardware is used in the existing OBCS system. System reliability is ensured by using IP network technologies that provide redundancy. The new OBCS system was first installed to observe the NiigataKobe tectonic zone in the Japan Sea on September 2010. Although this first OBCS system has a total length of 25 km, it has been proven that seismic data can be successfully obtained and that the new OBCS system is effective and useful for the dense observation of seismogenic activities on the sea floor around Japan. key words: OBCS, earthquake

Capability of the penetrator seismometer system for lunar seismic event observation

We developed a seismometer system for a hard landing “penetrator” probe in the course of the former Japanese LUNAR-A project to deploy new seismic stations on the Moon. The penetrator seismometer system (PSS) consists of two short-period sensor components, a two-axis gimbal mechanism for orientation, and measurement electronics. To carry out seismic observations on the Moon using the penetrator, the seismometer system has to function properly in a lunar environment after a hard landing (impact acceleration of about 8000 G), and requires a signal-to-noise ratio to detect lunar seismic events. We evaluated whether the PSS could satisfactorily observe seismic events on the Moon by investigating the frequency response, noise level, and response to ground motion of our instrument in a simulated lunar environment after a simulated impact test. Our results indicate that the newly developed seismometer system can function properly after impact and is sensitive enough to detect seismic events on the Moon. Using this PSS, new seismic data from the Moon can be obtained during future lunar missions.

Slow flow solutions and chaos control in an electromagnetic seismometer system

We study in this paper the dynamics and chaos control of a non-linear electromagnetic seismometer system consisting of an extended Duffing electrical oscillator magnetically coupled with a natural Duffing mechanical oscillator. The singular perturbation method is used to find slow solutions. Some bifurcation structures and the variation of the corresponding Lyapunov exponent are obtained. Transitions from a regular behavior to chaotic orbits are seen to occur for large amplitudes of the external excitation. We also examine the application of a simple adaptive damping feedback controller to eliminate the chaotic behavior in a controlled extended Duffing system. The main idea is to regulate the chaotic motion of the electromagnetic seismometer system around less complex attractors, such as equilibrium points and periodic orbits. The effectiveness and efficiency of the proposed feedback control strategy is illustrated by means of numerical simulations.

P08 1985 年以降房総沖海底地震地震計で観測された T 相について

P08 1985 年以降房総沖海底地震地震計で観測された T 相について

Amplitude response of a telemetered seismic system from seismometers to digital acquisition system

Automated amplitude response of the complete seismometer, telemetry and recording system js obtaiued trom sinusoidal inputs to the calibration coil. Custom-built software was designed to perform fully automatic cali- bration analyses of the digital signals. In this paper we describe the signals used for calibration and interactive and batch procedures designed to obtain calibration functions in automatic mode. By using a steady-state method we reach a high degree of accuracy in the determination of both the frequency and amplitude of the \ignal. The only parameters required by this procedure are the seismometer mass, the calibration-coil constant and the intensity of the current injected into the calibration coil. This procedure is applicable to telemetered seismic systems and represents an optimization of the processing time. The software was designed to requjre no modification" jf the device used to generate the sinusoidal current should change. In particular, it is possi- ble to changc the number of monotrequcncy packages transmitted to the calibration coil with the on]y restric- tion that the difference between the frequency of two consecutjve packages be greater than 5%; for these rea- sons the procedure is expected to be usefu] for the seismological community. The paper inc]udes a generaI de- scription of thc designing criteria, and of the hardware and software architecture, as well as an account of thc system's performancc during a two year period of operation.

Instrument calibration of ocean bottom seismographs

To increase the accuracy of measuring sea floor motion with ocean bottom seismometers, we calibrate the seismometer system on the ocean floor. Data from the sea floor calibration, augmented with electronic and land calibration data, enables us to find the OBS transfer function to an accuracy of 0.5% in the frequency range of 0.1 to 32 Hz. We are able to distinguish between temperature, instrument and OBS ground coupling effects, all of which alter the transfer function. This paper reviews our method of calibration and discusses the effects of temperature and some of the instrument design features on the vertical seismometer transfer function.

発破によつて誘発される微小破壊

The mechanism generating the micro-fractures in the mine was investigated.The micro-fractures occurring immediately after an explosion were observed for about an hour at the Nakatatsu mine in Fukui prefecture in 1982. The depth of the explosion point was about 700m. The velocity of P-wave near the observation site was 6.32km/s. Three accerelation-type seismometers and ten velocity-type seismometers were placed three-dimensionally surrounding the explosion point. The average span between seismometers was about 50m. The accerelation response of the accerelation-type seiemomenter system is flat up to 10kHz and the velocity response of the velocity-type seismometer system is flat up to about 1kHz.The relative foci to the explosion point were solved from the travel time residuals between the explosion and the micro-fractures. The hypocenters concentrated near one of the corners of the newly excavated face.The mechanism solution of the micro-fractures is normal-fault type, which indicates that the micro-fractures were generated by the compressional stress in the vertical direction.The micro-fractures occuring immediately after an explosion are generated by the stress concentration, that the load of the upper mass which had been supported by the rock which was excavated with the explosion concentrates near the corner of the newly excavated face.

Seismic system calibration: 1. Parametric models

abstractWe describe linear models of the IDA (International Deployment of Accelerometers) and SRO (Seismic Research Observatories) feedback seismometers obtained by straightforward analysis of the control systems. The most important property of these models is the theoretical transfer function they yield, relating Earth acceleration to output voltage. The parameterization of the theoretical transfer function is described. Several uses of the system models and transfer function are discussed, but we conclude that the parameterized models do not provide a sufficiently accurate means of describing the installed accelerometer's behavior. A speedier, more automatic and more accurate calibration can be obtained by electrically perturbing the seismometer system. This technique is discussed in Part 2.

Seismology on Mars

A three-axis short-period seismometer has been operating on the surface of Mars in the Utopia Planitia region since September 4, 1976. During the first 5 months of operation, approximately 640 hours of high-quality data, uncontaminated by lander or wind noise, have been obtained. The detection threshold is estimated to be magnitude 3 to about 200 km and about 6.5 for the planet as a whole. No large events have been seen during this period, a result indicating that Mars is less seismically active than earth. Wind is the major source of noise during the day, although the noise level was at or below the sensitivity threshold of the seismometer for most of the night during the early part of the mission. Winds and therefore the seismic background started to intrude into the nighttime hours starting on sol 119 (a sol is a Martian day). The seismic background correlates well with wind velocity and is proportional to the square of the wind velocity, as is appropriate for turbulent flow. The seismic envelope power spectral density is proportional to frequency to the −0.66 to −0.90 power during windy periods. A possible local seismic event was detected on sol 80. No wind data were obtained at the time, so a wind disturbance cannot be ruled out. However, this event has some unusual characteristics and is similar to local events recorded on earth through a Viking seismometer system. If it is interpreted as a natural seismic event, it has a magnitude of 3 and a distance of 110 km. Preliminary interpretation of later arrivals in the signal suggest a crustal thickness of 15 km at the Utopia Planitia site which is within the range of crustal models derived from the gravity field. More events must be recorded before a firm interpretation can be made of seismicity or crustal structure. One firm conclusion is that the natural background noise on Mars is low and that the wind is the prime noise source. It will be possible to reduce this noise by a factor of 103 on future missions by removing the seismometer from the lander, operation of an extremely sensitive seismometer thus being possible on the surface.

Dashti Biaz, Iran, Earthquake of August 1968

A THREE-COMPONENT seismometer system was sited on limestone 15 km north of Dashti Biaz (marked AA in Fig. 1). The site was comparatively free from noise and enabled the record and playback systems to operate at a gain of more than four million at the centre frequency of the small aftershocks (10 Hz) and record most of the activity in the area.

Ocean-bottom seismograph

In one program of Project VELA UNIFORM, the Air Force Cambridge Research Laboratories and Texas Instruments developed the ocean-bottom seismograph as a research tool for the study of acoustical wave energy at the solid earth-water interface generated either by earthquakes or by explosive sources. The seismograph described by this article is a third-generation unit having progressed through more than four years of development, design, and field experiments. The present configuration is spherical, 40 inches in diameter. It has been tested successfully in various locations to a depth of 24 000 feet. The primary components, in addition to the three-component seismometer system, contained within the seismograph are a digital clock having a 40-day capacity, with 0.1 second accuracy, seismic amplifiers capable of detecting noise level of 0.1 microvolt or less, a magnetic tape transport having a 30-day recording capacity for signals of less than 10 c/s frequency, and internal battery power supply for all components. In operation, the seismograph descends to the desired depth free fall, remains unattended and untethered, and is retrieved on sonar code command or preset time by decoupling the anchor base through a cocked spring mechanism, which is triggered by fusion of a small steel wire. Results to date have proved the feasibility of such an ocean-bottom data system, including the important capability to recall the package by sonar code command.

Processing of seismic data from an automatic digital recorder

Abstract Data from a three-component, long-period seismometer system is recorded in digital form on magnetic tape by a device which has been described by Miller. Preliminary editing and processing is performed to select events of interest from the 24-hour tapes and place them on a library tape that is compatible with a computer. Emphasis is placed on location, correction, and flagging of errors that occur during the recording and editing process. Processing routines developed include: correction for seismometer response, orbital motion functions, energy computation, band pass filtering for mode separation, etc. The dynamic range of the system is 86 db and the response is adequate over the range .02 to 2.0 cps. For the purpose of detailed analysis, digital records from this system are superior to paper records from any of the existing seismographs in use at this laboratory. The main disadvantage of data in this form is the difficulty of inspecting signals by eye in order to make preliminary interpretations.