Probability density function for Opende 22-02-2020 event

The Opende event on 22-02-2020:18:12:55.2 with a local magnitude of 1.42 was detected by the KNMI network (KNMI, 1993) and located near-real time with the Hypocenter method (Lienert et al., 1986). This fast solution uses an average 1D model for the north of the Netherlands (Kraaijpoel and Dost, 2013). Here the epicenter is improved by using a best-fitting traveltime versus distance model based on a database of local P-wave traveltime picks. This data-driven model naturally incorporates actual underburden velocities and only well pickable phase arrivals. An error estimate is derived from the spread in picking times from the best-fitting model. This error incorporates both the local variations of the velocity field as well as picking errors. These errors are propagated further into an epicentral probability density function (PDF). This results into an updated epicenter and its 95% confidence region. For post-2014 events within the Groningen network, also an updated hypocenter solution is available (Spetzler et al., 2018).