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Temperature dependence of broadband seismometer sensitivity

Tomofumi Shimoda, Wataru Kokuyama, Hideaki Nozato

Abstract

Broadband seismometers are widely used in global observation networks deployed for geophysics research. Recently, the calibration of their sensitivity has become an important factor for ensuring observation accuracy. One of the limiting factors of calibration uncertainty is the temperature dependence of the sensitivity because seismometers operate in a wide range of temperatures. However, systems that accurately measure the temperature coefficient in seismometers have not been established. Herein, we develop such a system using a triaxial vibration exciter combined with a thermostatic chamber. Using this system, we calibrated several broadband seismometers (Trillium Compact, Trillium Horizon 360, and CMG-3T) at various temperatures, ranging from $-15 ^\circ$C to $+45 ^\circ$C. We found that the temperature coefficient was $(0.11\pm0.01)$ %/$^\circ$C, which can be attributed to the internal magnet of the seismometers. The variation of the phase delay corresponded to a change of less than 2 ms in output time delay. Additionally, we found that the relative frequency response below 1 Hz was stable against temperature variations. These values are useful for evaluating the measurement accuracy of seismometer observation networks.

Temperature dependence of broadband seismometer sensitivity

Abstract

Broadband seismometers are widely used in global observation networks deployed for geophysics research. Recently, the calibration of their sensitivity has become an important factor for ensuring observation accuracy. One of the limiting factors of calibration uncertainty is the temperature dependence of the sensitivity because seismometers operate in a wide range of temperatures. However, systems that accurately measure the temperature coefficient in seismometers have not been established. Herein, we develop such a system using a triaxial vibration exciter combined with a thermostatic chamber. Using this system, we calibrated several broadband seismometers (Trillium Compact, Trillium Horizon 360, and CMG-3T) at various temperatures, ranging from C to C. We found that the temperature coefficient was %/C, which can be attributed to the internal magnet of the seismometers. The variation of the phase delay corresponded to a change of less than 2 ms in output time delay. Additionally, we found that the relative frequency response below 1 Hz was stable against temperature variations. These values are useful for evaluating the measurement accuracy of seismometer observation networks.
Paper Structure (6 sections, 4 equations, 2 figures)

This paper contains 6 sections, 4 equations, 2 figures.

Table of Contents

  1. KEY POINTS
  2. Introduction
  3. Measurement method
  4. Absolute midband sensitivity calibration
  5. Relative frequency response measurement
  6. Measurement results

Figures (2)

  • Figure 1: Measurement setup for temperature coefficient of seismometer sensitivity.
  • Figure 2: Variation of the midband sensitivity with temperature of the Trillium Compact (top), Trillium Horizon 360 (center), and CMG-3T (bottom) seismometers. The upper half of each graph shows the measured values (points) and their linear fitting (lines). The lower half shows the deviation from the fitting.