Epicenters for the Lauwerzijl and Kommerzijl events on 17-11-2022

On 17-11-2022 two events occurred within one hour. The first event is the Lauwerzijl event at 11:27:43.79 UTC with a local magnitude of 1.7 , the second event is the Kommerzijl event at 12:18:37 UTC with a local magnitude of 1.1. Both events were detected by the KNMI network (KNMI, 1993) and located near-real time with the Hypocenter method (Lienert et al., 1986). These fast solutions use an average 1D model for the north of the Netherlands (Kraaijpoel and Dost, 2013).

In this report, the epicenters are improved by using a best-fitting traveltime versus distance model based on a database of local P-wave traveltime picks. This data-driven model 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 updated epicenters and their 95% confidence regions.

On 7-4-2018 there was a similar sequence of events at the Kommerzijl gas field. A M1.7 in Lauwerzijl (07:17:49.39 UTC) was followed by a M1.0 in Kommerzijl (08:25:05.79 UTC).