ANOMALOUS CRUSTAL MOVEMENTS PRIOR TO GREAT EARTHQUAKES AS DERIVED FROM TIDE-GAUGE RECORDS - THE MESSINA, 1908, I = XI, EARTHQUAKE CASE-HISTORY

Strain precursors prior to great earthquakes determined from tide gauge records worldwide are discussed. The records at four sites in the Tyrrhenian Sea (1883-1922) are used to identify an anomaly in the sea level before the catastrophic Messina earthquake of December 28, 1908, with I(o) = XI. There are pre-seismic, co-seismic and post-seismic phases in the crustal movements. The pre-seismic anomaly began at least 5-8 years before the event (DELTA-T greater-than-or-equal-to 5-8 yr) and occurred as far as 530-870 km (D greater-than-or-equal-to 530-870 km) from the epicentre. The strain precursors of this earthquake are compared with other similar cases and the worldwide relations of M-alpha-D and M-alpha-T.