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