Which earthquake occurred with a magnitude of 5.6 and led to the establishment of EarthScope's fault observatory?

The establishment of EarthScope's fault observatory is closely associated with the 5.6 magnitude earthquake that occurred in the Parkfield segment of the San Andreas Fault in California. This earthquake, which happened in 2004, was significant as it provided researchers with an opportunity to study the behavior of seismic faults in detail. The Parkfield segment has been the focus of scientific interest for many years because of its relatively regular history of moderate seismic activity, making it an ideal location for the deployment of monitoring equipment and instruments aimed at improving earthquake prediction models. EarthScope itself was designed to enhance the understanding of Earth's processes and improve the monitoring of seismic activity, highlighting the importance of the Parkfield earthquake in the context of earthquake science.