Hamiltonian Monte Carlo for the Purpose of Induced Source
Characterization: Application to an ML 3.4 Event in the Groningen Gas
Field
Abstract
Hamiltonian Monte Carlo (HMC) is known to be highly efficient when
sampling high-dimensional parameter spaces. This high efficiency can be
attributed to Hamilton’s equations, which guide the sampling of the
model space. In the case of weakly non-linear problems, this efficiency
can be increased even further by linearizing the forward problem. In
this study, we exploit this for the purpose of estimating source
parameters of a 3.4 magnitude induced event that originated in the
Groningen gas field in 2019. In total, we estimate ten earthquake
parameters: centroid (three coordinate components), moment tensor (six
elements), and origin time. We demonstrate that, in the absence of a
sufficiently accurate centroid prior, the linearization of the forward
model necessitates multiple initial centroid priors. Here, we consider
two sets of initial centroid priors. The first set is based on the known
fault geometry in the Groningen reservoir, whereas the second set is
obtained by placing initial centroid priors on a uniform horizontal grid
at a depth of 3 km (the approximate depth of the gas reservoir). In
general, the results from both sets are in good agreement with each
other. Most important, however, is their agreement with the geological
knowledge of the area: the posterior peaks for model vectors containing
a centroid near a major fault and a moment tensor that corresponds to
normal faulting along a plane which has a strike almost coinciding with
the strike of that major fault.