[1] We examine the potential triggering relationship between large earthquakes and methane mud volcano eruptions. Our data set consists of a 191-year catalog of eruptions from 77 volcanoes in Azerbaijan, central Asia, supplemented with reports from mud volcano eruptions in Japan, Romania, Pakistan, and the Andaman Islands. We compare the occurrence of historical regional earthquakes (M > 5) with the occurrence of Azerbaijan mud volcano eruptions and find that the number of same-day earthquake/ eruption pairs is significantly higher than expected if the eruptions and earthquakes are independent Poisson processes. The temporal correlation between earthquakes and eruptions is most pronounced for nearby earthquakes (within $100 km) that produce seismic intensities of Mercalli 6 or greater at the location of the mud volcano. This assumed magnitude/distance relationship for triggering observed in the Azerbaijan data is consistent with documented earthquake-induced mud volcano eruptions elsewhere. We also find a weak correlation that heightened numbers of mud volcano eruptions occur within 1 year after large earthquakes. The distribution of yearly eruptions roughly approximates a Poisson process, although the repose times somewhat favor a nonhomogenous failure rate, which implies that the volcanoes require some time after eruption to recharge. The volcanic triggering likely results from some aspect of the seismic wave's passage, but the precise mechanism remains unclear.

Geodynamic processes occurring in the upper mantle such as slab break off and lithosphere delamination often result in high rates of lithospheric deformation and rapid tectonic uplift of large areas. The continent-continent collision zone between Arabia and Eurasia has been widely studied in this context, but several different viable geodynamic models exist to explain the uplift and deformation of the Anatolian Plateau and the Caucasus Mountains. We have imaged the uppermost mantle shear wave velocity structure of the East Anatolian-Caucasus region using surface wave tomography to better understand the regional tectonic activity since the onset of the collision between the Arabian and Eurasian Plates. Furthermore, we used our tomographic models to better understand the processes, which are responsible for the formation of the 2 km high plateau and the widespread volcanism in eastern Turkey, as well as reactivation of deformation and deep seismicity in the eastern Greater Caucasus. Our model of regional upper mantle shear wave velocity structure supports subduction of the northern and southern branches of Neo-Tethys lithosphere between Eurasia and Gondwana and suggests a possible underthrusting of the Kura Basin lithosphere beneath the Greater Caucasus.

[1] The Anatolian plateau-Caucasus-Caspian region is an area of complex lithospheric structure accompanied by large variations in seismic wave velocities. Despite the complexity of the region, little is known about the detailed lithospheric structure. Using data from 31 new, permanent broadband seismic stations along with results from a previous 29 temporary seismic stations and 3 existing global seismic stations in the region, a 3-D velocity model is developed using joint inversion of teleseismic receiver functions and surface waves. Both group and phase dispersion curves (Love and Rayleigh) were derived from regional and teleseismic events. Additional Rayleigh wave group dispersion curves were determined using ambient noise correlation. Receiver functions were calculated using P arrivals from 789 teleseismic (30°-90°) earthquakes. The stacked receiver functions and surface wave dispersion curves were jointly inverted to yield the absolute shear wave velocity to a depth of 100 km at each station. The depths of major discontinuities (sediment-basement, crust-mantle, and lithosphere-asthenosphere) were inferred from the velocity-depth profiles at the location of each station. Distinct spatial variations in crustal and upper mantle shear velocities were observed. The Kura basin showed slow (∼2.7-2.9 km/s) upper crustal (0-11 km) velocities but elevated (∼3.8-3.9 km/s) velocities in the lower crust. The Anatolian plateau varied from ∼3.1-3.2 in the upper crust to ∼3.5-3.7 in the lower crust, while velocities in the Arabian plate (south of the Bitlis suture) were slightly faster (upper crust between 3.3 and 3.4 km/s and lower crust between 3.8 and 3.9 km/s). The depth of the Moho, which was estimated from the shear velocity profiles, was 35 km in the Arabian plate and increased northward to 54 km at the southern edge of the Greater Caucasus. Moho depths in the Kura and at the edge of the Caspian showed more spatial variability but ranged between 35 and 45 km. Upper mantle velocities were slow under the Anatolian plateau but increased to the south under the Arabian plate and to the east (4.3-4.4 km/s) under the Kura basin and Greater Caucasus. The areas of slow mantle coincided with the locations of Holocene volcanoes. Differences between Rayleigh and Love dispersions at long wavelengths reveal a pronounced variation in anisotropy between the Anatolian plateau and the Kura basin.

The lateral variations of seismic attenuation in the crust of Turkey and surrounding regions have been imaged from the inversion of interstation Lg Q-measurements.This study develops the first tomographic model for Lg Q 0 in this region. That model is consistent with previous more qualitative Lg-attenuation models that showed inefficient or blocked Lg across the Eurasian-Arabian plate boundary. In general, the northern Arabian platform has low to normal Lg Q 0 -values (ϳ250-350), whereas high Q 0 -values (ϳ670-800) occur in the southern Arabian Plate. Additionally, we have found a dramatic decrease in Lg Q 0 across the Bitlis suture, the plate boundary between the Arabian and Eurasian plates. Beneath the Turkish Plateau, our high to moderate Lg-attenuation values (Q 0 ϳ100-200) probably originates from both scattering and intrinsic attenuation due to the tectonic complexity and the widespread young volcanics in the region. We conclude that the lowest Q 0 -values for the East Anatolian plateau (ϳ70-100) and the portion of western Turkey around the Menderes Massif (ϳ60-150) are probably caused by intrinsic attenuation. We find low to normal Lg Q 0 -values (ϳ150-300) beneath the part of the Taurus Mountains in western Anatolia. These higher values may be related to the nature of the crust in the Tauride mountain belt. We also mapped the lateral variations in Lg g and observed a fairly consistent negative correlation between g and Lg Q 0 in the northern Middle East.