Geodetic measurements following the 23 October 2011, M w = 7.2 Van (eastern Turkey) earthquake reveal that a fault splay on the footwall block of the coseismic thrust fault was reactivated and slipped aseismically for more than 1.5 years following the earthquake. Although long-lasting aseismic slip on coseismic ruptures has been documented following many large earthquakes, long-lasting, triggered slip on neighboring faults that did not rupture during the earthquake has not been reported previously. Elastic dislocation and Coulomb stress modeling indicate that the postseismic deformation can be adequately explained by shallow slip on both the coseismic and splay fault and is likely driven mostly by coseismic stress changes. Thus, the slip deficit on the shallow section of the coseismic fault indicated by interferometric synthetic aperture radar-based models has been partially filled by aseismic slip, suggesting a lower likelihood for a large earthquake on the shallow section of the Van fault than suggested by previous studies.

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We described the first results of an on-going study of absolute gravity changes after the 17 August 1999 Izmit earthquake in Marmara region. Repeated absolute gravity measurements were carried out six stations with an A10 absolute gravimeter from 2009 to 2011 in the region. A gravimetric calibration baseline (of the range of about 415 milliGal (mGal), 1 mGal = 10 −5 ms −2 ) was established in the region for the purposes of the calibration of the relative gravimeters. The absolute gravity measurements, repeated twice a year (October, June), can resolve gravity changes with a precision better than 5 microGal (μGal)/yr interval.The absolute gravity stations indicate a statistically significant gravity decrease at one of the absolute gravity stations in the calibration baseline, but the other stations do not. Generally, the absolute gravity difference agrees well with the general trend of the relative gravity changes. In addition, the precise vertical gravity gradients with relative gravity measurements have been determined at the absolute gravity stations for the reduction of measured gravity to the benchmark. The gradients scatter around the nominal constant (3.086 μGal/cm) between 2.82-3.73 μGal/cm as a result of the local density anomalies. The difference from the nominal gradient causes the error around 7-14 μGal by applying the normal vertical gradient instead of the directly measured one.