Publication Date:
2016-10-01
Description:
We re-evaluate the 72 year history of surface slip on the North Anatolian Fault at Ismetpasa since the Mw = 7.4 1944 Bolu/Gerede earthquake. A revised analysis of published observations suggests that days after the earthquake the fault had been offset by 3.7 m, and 6 years later by an additional 0.74 m. Creep was first recognized on the fault in 1969 as a 0.13 m offset of a wall constructed in 1957 that now (2016) has been offset by 0.52 m. A carbon-rod creep-meter operated across the fault in the past two years confirms results from an invar-wire creep-meter operated 1982-1991 that surface slip is episodic. Months of fault inactivity are interrupted by slow slip (≤10 µm/day) or multiple creep events with cumulative amplitudes of 2-10 mm, durations of several weeks, and with slip-rates briefly exceeding 〉2.5 mm/hour. Creep events accommodate 80% of the surface slip and individually release ≈ 10 -6 shear-strain on the flanks of the uppermost 3-7 km of the fault. GPS and InSAR methods yield a current fault slip rate of 7.6 ± 1 mm/yr suggesting that creep-meters incompletely sample the full width of the surface shear zone. The slip rate has slowed from 〉10 mm/yr in 1969 to 6.1 mm/year at present, 4.65 mm/yr of which appears to be due to steady interseismic creep driven by plate boundary stressing rates. We calculate that a further 1 m of aseismic surface slip will precede the next major earthquake on the fault assuming a ≈ 260 year mainshock recurrence interval on this segment.
Print ISSN:
0148-0227
Topics:
Geosciences
,
Physics
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