Seismology has a rich tradition of amateur participants.
It is relatively easy to acquire the necessary materials and build your own seismometer. The University of Northern Colorado has put together a nice Web page for constructing a simple seismometer. Simple Seismometer for Classroom Use The Seismological Society of America has a list of other resources for building your own seismograph and includes sources of materials. The Public Seismic Network is a organization of individuals interested in seismology. They have plans, software, and data to share.