This paper describes the cooperative interpretation of data from a global network of seismic stations in the context of nuclear test ban treaty verification. The problem, as solved by humans, involves the cooperation of a community of seismologists and the intellectual mechanism of assumption-based reasoning. Our computational agents cooperate by exchanging partial results that act as clues or heuristics about what assumptions to make and where to apply computationally expensive signal-processing algorithms, thus improving the quality of the global solution.