CASE HISTORY OF AN ANTICIPATED EVENT: The MAJOR (mw = 7.0, Mw =7.2) VRANCEA (ROMANIA) EARTHQUAKE OF 1986 – REVISITED

VASILE I. MÂRZA 1, VALERIU BURLACU 2, AURELIAN PANTEA 3, ZINA MALITA 3

1 Currently with Seismological Observatory, University of Brasilia, DF, Brazil
2 Center for Monitoring Research, Arlington, VA
3 National Institute (R&D) for Earth Physics (NIEP), Bucharest, Romania


Vrancea Seismogenic Zone (VSZ) is a conspicuous active area in terms of its: (A) extraordinary seismotectonic features [e.g.: extremely compact subcrustal source, impressive seismic moment release rate ( 10 N·m per 100 km per 100 yr), striking secludedness from other subcrustal sources, etc.]; (B) outstanding persistent and highly recurrent seismicity displaying a remarkable regularity in occurrence of large events and manifestation of a plethora of (geo)physical precursors; (C) severe socio-economic impact (i.e., 4 or 5 damaging events a century) with huge felt and meizoseismal area. The last two major VSZ events, that is, the 1977 (Mw = 7.5(HRV)) and the 1986 (Mw = 7.2(HRV)) were successfully forecasted and, respectively, anticipated. The forecasting (long-term earthquake prediction) of the 1977 event was based on the salient regularity patterns in long-term strong seismicity recurrence (cyclicity) displayed by all large events (Mw > 7) during a time span more than a millennium. In respect with the 1986 event, a further step was done, its anticipation (medium-term earthquake prediction) was based on a variety of precursory seismicity patterns (´a priori` reported), including: cyclicity (paired occurrences), pre-seismic quiescence, hypocentral migration/progression, b-slope change, etc.; but also other precursors: seismic (e.g., foreshocks), geophysical (an underground micro-temperature anomaly, or a telluric current observation), parameterized earthquake precursors algorithms, or even anomalous biosystem behaviour were reported in hindsight. Finally it should be emphasized the steady progress achieved in prediction of the recent major VSZ earthquakes and the good prospects towards earthquake prediction research in this very unique seismogenic zone of the World.

Key words: intermediate-depth earthquake, precursors, Vrancea