Monitoring earthquakes with gravity meters

Seismic waves from a magnitude 8.3 earthquake in Japan were consistently recorded by five nearly identical gPhone gravity meters in Colorado. Good correlation was also found in the response of two different types of gravity meters and a standard seismometer in Walferdange, Luxembourg to an earthquake of magnitude 8.2 in Japan, indicating that all of them were capable of measuring the surface waves reliably. The gravity meters, however, recorded 11 separate arrivals of Raleigh waves, while the seismometer only one. Thus the gravity meters may be useful for obtaining new information in the study of seismic velocities, attenuation and dispersion.

A new PC control software for ZLS-Burris gravity meters

The previous operation of the ZLS-Burris gravity meter using a PDA already provides a significant improvement of the operation of a metal spring gravity meter. But in the practical field work the observer usually wishes more information about the measurement and the collected data. This situation sug- gested an improvement of the software and computer hardware. The goal was to develop a small useful PC tool that eliminates these deficits. However, it resulted in a very extensive application software, which was developed during 2011-2015. Along the way, some unwanted effects of the original control circuit were detected. Therefore as a last step a complete new control circuit for the feedback system was developed. This new circuit is fast and smooth and without resonance effects to the system. The algorithm parameters can be specifically adapted to the specific gravity meter. The software has a security system that ensures the user, depending on his level of knowledge, a limited access to the software options. Furthermore, a customer project management system is integrated. The observer, the gravity meters, the projects and maps can be assigned. Several ZLS Burris gravity meters can be managed. A large station data management is integrated. Every station has up to more than twenty parameters, such as the mandatory coordinates or supplementary pictures of the station. External storage and documentation of the measurements are possible with extra modules. In addition the maintenance of the gravity meter system is significantly improved. The motor control of the early ZLS Burris gravity meter is also improved. The complete rotation is displayed on the screen. Finally, two survey examples show the advantages of the software related to the accuracy and the time needed for a measurement.

An unidentified geophysical event recorded with L&R-ET gravity meter at Zhongshan Station,Antarctica

An unidentified geophysical event is first reported in this paper. It was recorded with Lacoste & Romberg earth tide gravity meter (ET 21) at Chinese Antarctic Zhongshan Station.

High Precision Absolute Gravity Meter Based on Time-to-Digital Conversion in FPGA

This paper proposes a novel method to design a high precision portable gravity acceleration meter on the Field Programmable Gate Array(FPGA)platform.Two technologies are used in FPGA to improve the time measurement accuracy to 54 ps and the measurement accuracy of g to the level of 1μGal(1 Gal=1 cm/s^(2)).The one is the proposed clock rising edge counting method for measuring the coarse time,in which the measured coarse time resolution can reach 5 ns by setting the clock frequency up to 200 MHz.The other is the realization of the time-to-digital conversion(TDC)circuits in FPGA which can further improve the time measurement accuracy to 54 ps.In the TDC circuit,we analyze the influence of the frequency stability of crystal oscillator and the distance of infrared tube on the measurement accuracy of g.The increase of frequency stability(10^(–9)to 10^(–11))can greatly improve the measurement accuracy of g(5.8143 to 2.0799μGal),but further increase of frequency stability(10^(–11)to 10^(–12))has little effect on improving the accuracy of g.Through analysis and simulation,it is found that the setting of distance between laser pair also has a great influence on the accuracy of g.Only when the distance is set to the optimal,we can make the accuracy of g the highest.In this paper,the method of obtaining the best distance and the corresponding accuracy of g are given.In addition,the proposed system uses Nios II soft core processor to implement all the controlling,calculation and display functions,which improves system integration,reduces system cost and meets the needs of field geological survey and gravity prospecting.

Feasibility study applied to mapping tidal effects in the Pannonian basin--An effort to check location dependencies atμGal level

This paper summarizes the main instrumental and methodological points of the tidal research which was performed in the framework of the National Scientific Research Fund Project K101603. Since the project is still running the tidal analysis results published here are only preliminary. Unmodelled tidal effects have been highlighted in some recent absolute gravity measurements carried out in the Pannonian basin resulting in a periodic modulation exceeding the typical standard deviations （±1microGal） of the drop sets. Since the most dominant source of the daily gravity variation is the bulk tidal effect, the goal of the project is to check its location dependency at BGal level. Unfortunately Hungary has had no dedicated instrumentation, so an effort was made to make the available LaCoste- Romberg spring G meters capable for continuous recording. As a reference instrument the GWR SG025 operated in the Conrad Observatory, Austria was also used and in the mean time of the project, a Scintrex CG-5 became also available, Eventually 6 instruments at 5 different locations were operated for 3 9 months mainly in co-located configuration. Although many experiments （moving mass calibrations） were done to determine the scale factors and scale functions of the instruments, the direct comparison of the tidal parameters obtained from the observations is still questionable. Therefore the ratio of the delta factors of O1 and M2 tidal constituents was investigated supposing that M2 is much more influenced by the ocean loading effect than O1. The slight detected increase of δ（O1 ）/δ（M2） （≈0.2%） toward east does not contradict to theory. This result has to be validated in the near future by analyzing available ocean loading models.