Speakers
Description
Technical specifications for IMS stations require accuracy of calibration results to be within 5% and 5-degrees for amplitude and phase of the nominal response, respectively. Taking into consideration that the operating temperature for equipment components is specified between -20oC to +45oC, the sensors and dataloggers must assure operational quality within their nominal response specified and traced over the operational lifetime. However, it was noticed that ambient temperature variations may influence CALIB values acting as conversion factors to ground motion (McCormack, ECS/PRES/WGB-62/WEG/5). Despite protection measures undertaken, seasonal temperature variations at equipment vaults could reach up to tens of degrees. Therefore, such influence may impact event magnitude estimates calculated at the station. Observation of magnitude residuals (MR) at some IMS stations display seasonal variations, which could relate to temperature changes depending on sensor type, emplacement depth and vault insulation quality. The observed seasonal MR variations are found to be up to 0.25 magnitude units for mb and less prominent for Ms. If the observations are further confirmed, this may require a specification update for better vault insulation or the involvement of the IDC database CALRATIO parameter, reflecting a possible change of CALIB relative to its nominal (baseline) value based on local temperature measurements.
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