The document discusses seismic data networks, instruments, and data centers. It describes the different types of seismic networks including global, regional, local, temporary, and seismic arrays. It also discusses several major seismic data centers such as NEIC, ORFEUS, IRIS, ISC, GEOFON, EMSC, and EarthScope. Finally, it covers various seismic observables including translations (displacement, velocity, acceleration), strain, and rotations that seismometers are capable of measuring.