An underground laser strainmeter, crossing a fault in the Gran Sasso massif, is discontinuously operating since late May 1994, after a few years of mechanical stabilization of end monuments. Its main characteristics are: high sensitivity (Δl/l ≈ 3 × 10−12), large dynamic range (up to 10−4), fast sampling rate (2 kHz), and the capability of following strain rates as sharp as 7 × 10−5 s−1. A swift extensional strain transient reaching a peak of at least 1 microstrain occurred in about one month from the beginning of the operating time, followed by a four-month-long coarsely stable period, and a slower decay. On June 2nd 1994, in coincidence with two local earthquakes, permanent extensional offsets of about 10 ne have been recorded. A further aseismic slip of the same order of magnitude and sign has been observed about thirty minutes arter the last preceding local event, and ten minutes before the next following one. At the same time, the arrival of seismic waves from a distant earthquake has been recorded by the interferometer. No similar signal behaviour has been observed any more since then.
Attivazione e primi risultati dell’interferometro geodetico nel Laboratorio Nazionale del Gran Sasso
CRESCENTINI, LUCA;AMORUSO, ANTONELLA;
1996-01-01
Abstract
An underground laser strainmeter, crossing a fault in the Gran Sasso massif, is discontinuously operating since late May 1994, after a few years of mechanical stabilization of end monuments. Its main characteristics are: high sensitivity (Δl/l ≈ 3 × 10−12), large dynamic range (up to 10−4), fast sampling rate (2 kHz), and the capability of following strain rates as sharp as 7 × 10−5 s−1. A swift extensional strain transient reaching a peak of at least 1 microstrain occurred in about one month from the beginning of the operating time, followed by a four-month-long coarsely stable period, and a slower decay. On June 2nd 1994, in coincidence with two local earthquakes, permanent extensional offsets of about 10 ne have been recorded. A further aseismic slip of the same order of magnitude and sign has been observed about thirty minutes arter the last preceding local event, and ten minutes before the next following one. At the same time, the arrival of seismic waves from a distant earthquake has been recorded by the interferometer. No similar signal behaviour has been observed any more since then.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
