This paper describes a distributed system called Distributed Seismic Unix (DSU). DSU provides tools for creating and executing application sequences over several types of multiprocessor environments. DSU is designed to assist geophysicists in developing and executing sequences of Seismic Unix (SU) applications in clusters of workstations as well as on tightly coupled multiprocessor machines. SU is a large collection of subroutine libraries, graphics tools and fundamental seismic data processing applications that is freely available via the Internet from the Center for Wave Phenomena (CWP) of the Colorado School of Mines. SU is currently used at more than 500 sites in 32 countries around the world. DSU is built on top of three publicly available software packages: SU itself; TCL/TK, which provides the necessary tools to build the graphical user interface (GUI); and PVM (Parallel Virtual Machine), which supports process management and communication. DSU handles tree-like graphs representing sequences of SU applications. Nodes of a graph represent SU applications, while the arcs represent the way the data flow from the root node to the lead nodes of the tree. In general the root node corresponds to an application that reads or creates synthetic seismic data, and the leaf nodes are associated with applications that write or display the processed seismic data; intermediate nodes are usually associated with typical seismic processing applications like filters, convolutions and signal processing. Pipelining parallelism is obtained when executing single-branch tree sequences, while a higher degree of parallelism is obtained when executing sequences with several branches. A major advantage of the DSU framework for distribution is that SU applications do not need to be modified for parallelism; only a few low-level system functions need to be modified.