Abstract
10 M >= 6.7 earthquakes ruptured 1000 km of the North Anatolian fault
(Turkey) during 1939-1992, providing an unsurpassed opportunity to
study how one large shock sets up the next. We use the mapped surface
slip and fault geometry to infer the transfer of stress throughout
the sequence. Calculations of the change in Coulomb failure stress
reveal that nine out of 10 ruptures were brought closer to failure
by the preceding shocks, typically by 1-10 bar, equivalent to 3-30
years of secular stressing. We translate the calculated stress changes
into earthquake probability gains using an earthquake-nucleation
constitutive relation, which includes both permanent and transient
effects of the sudden stress changes. The transient effects of the
stress changes dominate during the mean 10 yr period between triggering
and subsequent rupturing shocks in the Anatolia sequence. The stress
changes result in an average three-fold gain in the net earthquake
probability during the decade after each event. Stress is calculated
to be high today at several isolated sites along the fault. During
the next 30 years, we estimate a 15 per cent probability of a M >=
6.7 earthquake east of the major eastern centre of Ercinzan, and
a 12 per cent probability for a large event south of the major western
port city of Izmit. Such stress-based probability calculations may
thus be useful to assess and update earthquake hazards elsewhere.
Users
Please
log in to take part in the discussion (add own reviews or comments).