Deploying and servicing a seismic network in Central Italy
BGS seismologists are using the seismicity that is hitting Central Italy to analyse the triggering and evolution of an earthquake sequence.02/06/2017 By BGS Press
From a scientific point of view, the seismicity that is hitting Central Italy presents itself as an unmissable opportunity for seismologists to analyse the triggering and evolution of an earthquake sequence. From the tens of instruments installed in the affected area, a huge amount of data are being collected. Such a well-recorded sequence will allow us to produce a comprehensive seismic catalogue of events. Using this quantity of data, new algorithms will be developed and tested for the characterisation of even the smallest earthquakes. Moreover, they will enable the validation of more accurate and testable statistical and physics-based forecast models.
2016 earthquake activity
The Central Apennines are one of the most seismically hazardous areas in Italy and in Europe. Many destructive earthquakes have occurred throughout this region in the past, most recently the 2009 magnitude 6.4 L’Aquila event. On 24 August 2016, just 43 km north of the 2009 epicentre, an earthquake of magnitude 6.0 occurred and devastated the villages of Amatrice and Accumoli, leading to 298 fatalities, hundreds of injured and tens of thousands of people affected. The main shock was followed under an hour later by a magnitude 5.4 aftershock.
Two months later, on 26 October, the northern sector of the affected area was struck by two earthquakes of magnitude 5.4 and 5.9 respectively, with epicentres near the village of Visso. To make things even worse, on 30 October the city of Norcia was hit by a magnitude 6.5 shock, which has been the biggest event of the sequence to date and the strongest earthquake in Italy in the last 36 years. Buildings collapsed and damage was very heavy in many villages, and many historical heritage buildings have reported irreparable damages, such as Norcia’s 14th century St Benedict Cathedral.
On 18 January 2017, four more earthquakes of magnitude greater than 5 were recorded near the villages of Montereale and Pizzoli, in the southern sector. Luckily, there have been no further fatalities since the very first event of 24 August 2016.
Immediately after the first big event, an emergency scientific response team was formed by BGS and the School of Geosciences at the University of Edinburgh, to support the rapid deployment of high-accuracy seismometers in collaboration with the Istituto Nazionale di Geofisica e Vulcanologia (INGV). The high detection capabilities, made possible by such a dense network, will let us derive a seismic catalogue with a great regional coverage and improved magnitude sensitivity. This new, accurate, catalogue will be crucial in developing operational forecast models. The ultimate aim is to understand the potential migration of seismic activity to neighbouring faults as well as the anatomy of the seismogenic structure and to shed light into the underlying physical processes that produce the hazard.
Thanks to the quick response of NERC and SEIS-UK, 30 broadband stations were promptly dispatched from Leicester and arrived in less than 48 hours in Rome. There, a group of nine people composed of INGV and BGS seismologists, technicians and PhD students from the University of Bristol, Dublin Institute for Advanced Study (DIAS) and University of Ulster were ready to travel across the Apennines to deploy the equipment. The first days in Rome were all about planning; the location of each station was carefully decided so as to integrate the existing Italian permanent and temporary networks in the most appropriate way. After having performed the ‘huddle test’ in the INGV storage room, which involves parallel checking of all the field instrumentation in order to ensure its correct functioning, all the equipment was packed up and the team headed to the village of Leonessa, a location considered safe enough to be used as the base camp (despite the village being damaged and partially evacuated after the 30 October event).
The seismic stations
Each seismic station is composed of a buried sensor, a GPS antenna, a car battery, a regulator and two solar panels. The current deployment will stay for the duration of the aftershocks’ activity and will be collecting data continually. Each sensor had to be carefully buried and levelled to guarantee the highest quality of recording, which was a strenuous challenge when the ground was quite rocky! Twenty-four stations were installed in an area of approximately 2700 km2.
As this type of seismic station didn’t have telemetry, each needed to be revisited to retrieve data. For this purpose, from 17 October 2016, David Hawthorn from BGS and Simone Mancini from the University of Bristol flew to Italy again and stayed there for the following ten days to service the seismometers and to do the first data dump. They also checked the quality of the first month of recordings, added a second solar panel where needed, and to prepare the stations for the forthcoming winter. To do that, a lot of hammering and woodworking was needed. David and Simone serviced all the sites, raising the solar panels and GPS antennas on posts, which were securely anchored to the ground, to prevent snow from covering them. The stations were all in good conditions, with just minor damage due to some very inquisitive cows.
Experiencing the seismicity
On 26 October, just the night before leaving for Rome, David and Simone experienced for themselves the frightening feeling of an earthquake just below their feet. Simone says:
Both the quakes of that evening surprised us while we were inside a building; the rumble just few seconds before the quake was shocking and the shaking was very strong. Fortunately, there were no severe damages in Leonessa but many people in the village refused to spend the night in their own houses. Also, it was impressive to see the local emergency services response: only a few minutes after the first quake, policemen were already out to patrol the inner village checking for any people experiencing difficulties.
Please contact David Hawthorn for further information.