Evidences for higher nocturnal seismic activity at the Mt. Vesuvius

TL;DR

This study reveals a consistent pattern of higher nocturnal seismic activity at Mt. Vesuvius, with variations linked to seasonal changes and a recent increase in daily oscillation amplitude, suggesting potential for improved volcanic hazard monitoring.

Contribution

It provides the first detailed analysis of diurnal seismic activity variations at Mt. Vesuvius using long-term data and proposes a new seismic activity index for hazard assessment.

Findings

Seismic activity is higher at night than during the day.

The amplitude of daily seismic oscillations varies seasonally, increasing in summer.

The daily oscillation amplitude has been increasing since 2008.

Abstract

We analyze hourly seismic data measured at the Osservatorio Vesuviano Ovest (OVO, 1972-2014) and at the Bunker Est (BKE, 1999-2014) stations on the Mt. Vesuvius. The OVO record is complete for seismic events with magnitude M > 1.9. We demonstrate that before 1996 this record presents a daily oscillation that nearly vanishes afterwards. To determine whether a daily oscillation exists in the seismic activity of the Mt. Vesuvius, we use the higher quality BKE record that is complete for seismic events with magnitude M > 0.2. We demonstrate that BKE confirms that the seismic activity at the Mt. Vesuvius is higher during nighttime than during day-time. The amplitude of the daily oscillation is enhanced during summer and damped during winter. We speculate possible links with the cooling/warming diurnal cycle of the volcanic edifice, with external geomagnetic field and with magnetostriction that should also stress the rocks. We find that the amplitude of the seismic daily cycle changes in time and has been increasing since 2008. Finally, we propose a seismic activity index to monitor the 24-hour oscillation that could be used to complement other methodologies currently adopted to determine the seismic status of the volcano and to prevent the relative hazard.