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Calibration Techniques in the Manufacture and Field Use of Seismic Instruments

Description: 

Calibration of seismic networks relies on cooperation of manufacturers, network operators, and certified laboratories. These parties must work together to measure key instrument parameters, quantifying errors that affect accuracy and precision, ideally with traceability to SI standards. Some techniques used in manufacturing cannot be used in the field, such as calibration at the internal sub-assembly or component level. Some techniques must be applied in the field to reconfirm correct in-situ operation, quantify any change in parameters due to aging or equipment degradation, and optionally apply corrections for environmental variables such as temperature. Testing seismic instruments at certified laboratories provides an independent reference.

Considerations in the manufacturing process include: (1) Uncertainties: how they arise and the impact on accuracy and precision; (2) Calibration methodologies available and their practical implementation; (3) Quality assurance in the factory calibration process; (4) Metrics to consider: sensitivity, relative transfer function, timing, calibrator features, alignment.

We discuss how these methods can be adapted for field use, with a focus on two challenges:

(1) Electrical versus ground motion calibration. Electrical calibration measures some parameters more accurately, but does not provide an independent measurement of all parameters. Ground motion should ideally be the measure of seismic performance, but has large errors in practice due to factors such as difficulty in separating site response from instrument response. We propose a combination of techniques, with use of multiple sensors to cross-check measurements.

(2) Temperature dependence of instrument sensitivity, as recently highlighted in two presentations at AGU 2024 (Slad; Shimoda). This is attributable to temperature dependence of permanent magnets used in force-feedback seismic sensors. This small effect can be characterized, and corrected if desired by periodically updating sensitivity metadata, using modern seismic sensors that include an internal temperature reporting capability.

Session: Fifty Years and Beyond of Broadband Seismic Instrumentation: Performance, Precision and Uncertainties - I

Type: Oral

Date: 4/16/2025

Presentation Time: 05:30 PM (local time)

Presenting Author: Geoffrey

Student Presenter: No

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