We present the LOTOS-07 code for performing local earthquake tomographic inversion, which is freely available (see the Data and Resources section for the Web site). The initial data for the code are the arrival times from local seismicity and coordinates of the stations. It does not require any information about the sources. The calculations start from absolute location of sources and estimates of an optimal 1Dvelocity model. Then the sources are relocated simultaneously with the 3D-velocity distribution during iterative coupled tomographic inversions. The code allows results to be compared based on node or cell parameterizations. The synthetic dataset used for testing the code is based on source-receiver configurations from a real experiment in Costa Rica. The travel times for this dataset are computed by 3D tracing through a rather complicated synthetic model and are perturbed with realistic noise. We also present a series of synthetic datasets with unknown sources and velocity models (see the Data and Resources section for the Web site) that can be used as blind benchmarks for testing different tomographic algorithms. We encourage other users of tomography algorithms to join the program on creating benchmarks that can be used to check existing codes.

[1] A model of seismic P and S anomalies in the upper mantle beneath Asia (in limits of 35°E-140°E, 12°N-57°N) was constructed based on the tomographic inversion of traveltime data from the revised ISC catalog for the years 1964-2004. The inversions were performed independently in 32 overlapping circular windows that cover the entire study area. The free inversion parameters in each window were defined individually depending on the available data based on synthetic modeling. Such adaptive tuning of parameters enables more optimal usage of the input data in areas with inhomogeneous ray coverage compared to global inversions. This approach resolves high-frequency patterns but is less sensitive to large anomalies with sizes comparable to the window diameter. Thus, this approach is somewhat similar to high-frequency filtration of the velocity distribution. The resolution capacity of the model was tested using checkerboard tests with various pattern sizes. To assess the role of random noise, independent test inversions of two data subsets (with odd and even numbers of events) were performed. Clear reconstructions of known structures, such as subducting plates beneath the Japan and Ryukyu arcs whose locations and shapes have been constrained by other studies, further indicate the reliability of the model. The 3-D models of P and S anomalies presented in horizontal and vertical sections show complex interactions of the lithospheric segments beneath the Alpine-Himalayan orogenic belts. Particular attention is focused on the collisional areas of Iran, Pamir-Hindukush, Tien-Shan, and Burma. The digital version of the 3-D P and S models is available at http://www.ivan-art.com/science/REGIONAL. Citation: Koulakov, I. (2011), High-frequency P and S velocity anomalies in the upper mantle beneath Asia from inversion of worldwide traveltime data,

[1] Here we present the results of local source tomographic inversion beneath central Java. The data set was collected by a temporary seismic network. More than 100 stations were operated for almost half a year. About 13,000 P and S arrival times from 292 events were used to obtain three-dimensional (3-D) Vp, Vs, and Vp/Vs models of the crust and the mantle wedge beneath central Java. Source location and determination of the 3-D velocity models were performed simultaneously based on a new iterative tomographic algorithm, LOTOS-06. Final event locations clearly image the shape of the subduction zone beneath central Java. The dipping angle of the slab increases gradually from almost horizontal to about 70°. A double seismic zone is observed in the slab between 80 and 150 km depth. The most striking feature of the resulting P and S models is a pronounced low-velocity anomaly in the crust, just north of the volcanic arc (Merapi-Lawu anomaly (MLA)). An algorithm for estimation of the amplitude value, which is presented in the paper, shows that the difference between the fore arc and MLA velocities at a depth of 10 km reaches 30% and 36% in P and S models, respectively. The value of the Vp/Vs ratio inside the MLA is more than 1.9. This shows a probable high content of fluids and partial melts within the crust. In the upper mantle we observe an inclined low-velocity anomaly which links the cluster of seismicity at 100 km depth with MLA. This anomaly might reflect ascending paths of fluids released from the slab. The reliability of all these patterns was tested thoroughly.Citation: Koulakov, I., et al. (2007), P and S velocity structure of the crust and the upper mantle beneath central Java from local tomography inversion,

An understanding of the formation of large magmatic reservoirs is a key issue for the evaluation of possible strong volcanic eruptions in the future. We estimated the size and level of maturity of one of the largest volcanic reservoirs, based on radial seismic anisotropy. We used ambient-noise seismic tomography below the Toba caldera (in northern Sumatra) to observe the anisotropy that we interpret as the expression of a fine-scale layering caused by the presence of many partially molten sills in the crust below 7 kilometers. This result demonstrates that the magmatic reservoirs of present (non-eroded) supervolcanoes can be formed as large sill complexes and supports the concept of the long-term incremental evolution of magma bodies that lead to the largest volcanic eruptions.