This paper describes the seismic events during water flooding into a shaft at the Saar mine, Germany. The Saar mine (Primsmulde field) experienced strong seismic events while coal mining by a double panel. Parts of the mine had to close after a ML = 4.0 event in 2008. No further seismic events occurred after mine closure. Starting in 2013, water from adjacent mine fields was let into at the main shaft and the water level in the shaft rose to 355 m above its base. Almost immediately seismic events were recorded by the surface seismic network. After an ML = 2.8 event the water level was held constant and only a few events of lower magnitudes were recorded. This paper focuses on the overall spatial distribution of the seismic events and compares them with the localized events from coal mining. Special focus is placed on water level in the shaft and assumptions about the water level/pore pressure distribution in the mine.
Coal mining in the Saar mining district (Primsmulde field) was accompanied by strong seismic events from the beginning. The series culminated in a Ml = 4.0 event with a peak particle velocity PPV of 94 mm/s on 2008 February 23. Mining was stopped immediately. One more seismic event occurred next day, but then no further events were recorded. Coal mining took place by the longwall panel method, here a double panel with an overall width of 700 m. The coal seam is slightly inclined (∼ 12°) across the panels, features a wide syncline along the panels and has an average depth overburden of 1411 m. The in-situ stresses from HydroFrac tests are estimated to be σv = 37.4 MPa, σh = 20.7 MPa and σH = 43.2 MPa. The major horizontal stress (σH = 43.2 MPa) is oriented perpendicular to the long axis of the longwall panels. The rock mass at mining depth and at the bottom of the nearby shaft was described being "bone-dry".
