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A recent dramatic increase in seismicity in the midwestern United States may be related to increases in deep wastewater injection. Here, we demonstrate that areas with suspected anthropogenic earthquakes are also more susceptible to earthquake-triggering from natural transient stresses generated by the seismic waves of large remote earthquakes. Enhanced triggering susceptibility suggests the presence of critically loaded faults and potentially high fluid pressures. Sensitivity to remote triggering is most clearly seen in sites with a long delay between the start of injection and the onset of seismicity and in regions that went on to host moderate magnitude earthquakes within 6 to 20 months. Triggering in induced seismic zones could therefore be an indicator that fluid injection has brought the fault system to a critical state. [ABSTRACT FROM AUTHOR]

Seismotectonics of the two recent earthquakes, one Mw 6.3 in the Bhutan Himalaya on 21 September 2009 and the other Mw 5.1 in the Assam valley on 19 August 2009, are examined here. The recent seismicity and fault plane solutions of these two felt earthquakes suggest that both the events occurred on the Kopili fault zone, a known active fault zone in the Assam valley, about 300 km long and 50 km wide. The fault zone is transverse to the east-west Himalayan trend, and its intense seismicity indicates that it transgresses into the Himalaya. The geologically mapped curvilinear structure of the Main Central Thrust (MCT) in the Himalaya, where the epicentre of the Bhutan earthquake is located, is possibly caused by the transverse Kopili fault beneath the MCT. This intensely active fault zone may be vulnerable to an impending larger earthquake (M > 7.0) in the region. [ABSTRACT FROM AUTHOR]

The North Anatolian Fault (NAF) forms the northern boundary of the Anatolian plate and is characterized by a right-lateral strike slip motion. The fault extends between 26° and 40° E longitudes and forms a broad arc roughly parallel to the coast of the Black Sea following a former suture zone. The only visible perturbations to the smooth geometry of the NAF are, at around 34-37°E longitude, two main splay faults named Ezinepazar-Sungurlu Fault and Suluova Fault with several related minor fault segments that bifurcate from the main fault line, possibly due to the convexity of the NAF geometry. These secondary fault structures show remarkable morphological expressions accompanied with elongated basin formations and significant microseismicity. The NAF, together with these splay faults, form a broad wedge-shaped shear zone called Amasya Shear Zone (ASZ) where major growing cities of central Anatolia such as Amasya, Çorum and Tokat are located. These cities, which today have total a population close to 500000 with significant industrial infrastructure, were subject to destructive earthquakes during both historical (such as 1579, 1794 and 1668) and instrumental (such as 1939, 1942a, 1942b, 1943 and 1996) seismic periods. Recent paleoseismological studies revealed the rupture history of NAF in a time span of 2000 years (for a review see Hartleb et al. 2006). However, the historical earthquake database of the study area contains unlocated destructive earthquakes (such as 1579 and 1794 events) which are proposed to be nucleated on the splay faults of the ASZ. This statement reveals that there is an unevaluated seismic hazard potential of the region. In this work, a 6 step procedure is followed for a complete earthquake hazard assessment for the study area: (1) First, the faults of ASZ are mapped in detail with field studies to understand the behavior and segmentation of the major fault systems (SuFS and EzSFS). (2) A detailed catalogue of instrumental seismic activity is prepared to understand the seismicity of the region and to define the local clusters concentrated on the fault segments. (3) Information of historical earthquakes are investigated through the literature and field study in major cities to identify the possible related fault segment, this is accomplished by comparing intensity distributions based on historical data and modeled scenarios. (4) The results of recently published analysis of a local GPS campaign (Yavasoglu et. al., 2009) is used to determine the annual slip rate resolved on the overall shear zone to estimate the earthquake recurrence interval. (5) For each active fault segment, the maximum magnitude of a possible earthquake is calculated with the relations between the rupture length and magnitude (Wells and Coppersmith, 1994). (6) GIS based earthquake scenarios based on attenuation relations (Tüysüz, 2003) are prepared to model the geographic intensity distribution for each calculated earthquake. … [ABSTRACT FROM AUTHOR]