Generating Uncertainty Distributions for Seismic Signal Onset Times

ABSTRACT Signal arrival-time estimation plays a critical role in a variety of downstream seismic analyses, including location estimation and source characterization. Any arrival-time errors propagate through subsequent data-processing results. In this article, we detail a general framework for refining estimated seismic signal arrival times along with full estimation of their associated uncertainty. Using the standard short-term average/long-term average threshold algorithm to identify a search window, we demonstrate how to refine the pick estimate through two different approaches. In both cases, new waveform realizations are generated through bootstrap algorithms to produce full a posteriori estimates of uncertainty of onset arrival time of the seismic signal. The onset arrival uncertainty estimates provide additional data-derived information from the signal and have the potential to influence seismic analysis along several fronts.

Short-duration infrasound signals observed at the array PVCI

<p>We present the most interesting cases from observations of short-duration infrasound signals at the array PVCI (50.53°N 14.57°E).  The array is equipped with three sensors and it has an aperture of 200 m. The optimum detection range of the array is 0.02-4 Hz.</p><p>On 24 August 2016 at 01:36:32 UTC, a strong earthquake occurred in Central Italy; the epicentre was located at 42.75°N and 13.22°E. The azimuth from PVCI to the epicentre was 187° and the distance was 871 km. At 02:23-02:40 UTC, signals from the azimuths around 195° were recorded at the array. The time interval corresponds to the expected stratospheric signal arrival.</p><p>On 3 March 2016 at 21:51-21:53 UTC, PVCI registered signal from the azimuth of 199°. The signal elevation was 30-35°. We assume that the signal source was the bolide EN060316 that entered the atmosphere above Upper Austria and Bavaria. </p><p>Two large accidental explosions occurred in the region recently; both of them were recorded by PVCI and other member stations of the CEEIN network. On 26-27 September 2017, an ammunition depot exploded in Kalynivka, Central Ukraine. Signals from the azimuths of 85-90° were recorded on 26 September 2017 at 21:02-21:05 UTC and at 23:16-23:21 UTC. On 1 September 2018 around 03:15 UTC, an explosion occurred in the refinery near Ingolstadt, Germany. A high amplitude signal arrived at PVCI at 03:30:48 UTC from the azimuth of 243°.</p>

Resolving VLBI correlator ambiguity in the time delay model improves precision of geodetic measurements

The modern Very Long Baseline Interferometry (VLBI) relativistic delay model, as documented in the IERS Conventions, refers to the time epoch when the signal passes one of two stations of an interferometer baseline (selected arbitrarily from the pair of stations and called the ‘reference station’ or ‘station 1’). This model consists of the previous correlation procedure used before the year 2002. However, since 2002 a new correlation procedure that produces the VLBI group delays referring to the time epoch of signal passage at the geocenter has been used. A corresponding correction to the conventional VLBI model delay has to be introduced. However, this correction has not been thoroughly presented in peer reviewed journals, and different approaches are used at the correlators to calculate the final group delays officially published in the IVS database. This may cause an inconsistency up to 6 ps for ground-based VLBI experiments between the group delay obtained by the correlator and the geometrical model delay from the IERS Conventions used in data analysis software. Moreover, a miscalculation of the signal arrival moment to the ‘reference station’ could result in a larger modelling error (up to 50 ps). The paper presents the justification of the correction due to transition between two epochs elaborated from the Lorentz transformation and the approach to model the uncertainty of the calculation of the signal arrival moment. Both changes are particularly essential for upcoming broadband technology geodetic VLBI observations.