My research interests, to date, have focused on regional seismology -- a broad field where one typically analyzes seismic signals recorded at a few tens of kilometers to a couple thousand kilometers to infer geologic structure of the Earth's upper layers, including the crust, to quantify the seismic sources and their implications on regional tectonics, and to characterize the nature of the seismic sources. The results of the analyses have diverse applications in earth science and they offer important contributions to our society and environment. For example, I analyzed regional seismic signals from earthquakes in Scandinavia to determine regional intraplate stress fields to evaluate earthquake hazard for nuclear power plants and for high-level nuclear waste depository. I analyzed regional signals in Eastern North America and in former Soviet Union to characterize various types of seismic source, which is an important issue in seismic monitoring for compliance of the comprehensive test ban treaty (CTBT).
I am the director of the Lamont-Doherty Cooperative Seismographic Network (LCSN) project which monitors earthquakes in the northeastern United States for evaluating earthquake hazards in the region and to understand better the occurrence of earthquakes in the stable continetal region. Since the summer of 1994, I have been working with my colleagues at the National Nuclear Center (NNC) of Kazakhstan in installation and operation of eight-station broadband seismographic network and a 21-element seismic array in Kazakhstan. These broadband stations and the array at very quiet sites provide some of the best observational seismic data in the world.
In recent years, I studied mechanism of earthquakes in Korea with my colleagues in Korea.