Three-dimensional tomographic inversion of the seismic velocity structure of the crust and upper mantle of northwestern Nicaragua

A three-dimensional tomographic image of the seismic velocity structure in the crust and upper mantle of northwestern Nicaragua was performed using the back-projection technique. The study is based on ~ 15,000 earthquakes located between 1975 and 1982 by the network installed by the USGS and the Institute of Seismic Research of Nicaragua. This data represents the longest continuous recording of seismicity by a homogeneous seismic network in Nicaragua. Data from this network has not been used before. Initially, a one-dimensional model of the seismic velocity structure (1-D) was determined in order to relocate the seismicity and to obtain a first estimate of the seismic velocity model of the continental crust. This 1-D crustal model was complemented with the upper mantle structure of the IASPEI91 Earth model. This initial 1-D model is used to iterate for a 3-D tomographic imaging of Nicaragua. The results show three distinct features. There is clear evidence of a low seismic velocity plume rising from the subducted slab at depths of between 60 and 120 km. This low-velocity zone may be interpreted as the high temperature melts originating in the slab and feeding the volcanic arc. In northern Nicaragua, a high-velocity region is identified beneath the coast that presumably reflects the thickness of the subducting oceanic plate, estimated to be approximately 50 to 60 km thick. Beneath the volcanic arc, there is a low seismic velocity zone extending from 10 to 20 km. This low-velocity zone is interpreted as high-temperature material in the crust feeding the magma chambers of the volcanic arc.