Analysis of the source parameters behaviour during the Val D'Agri test-injection (Italy)

Malta

Recent advances in understanding induced
earthquake mechanics are due to the new and

high-quality observations from seismic signals,
natural faults and laboratory experiments. The
synergy of different approaches allows the
acquisition of useful observations to understand
the earthquake source process. In this study we
investigate the source parameters behaviour of
induced earthquakes recorded during daily
injection tests in a wastewater disposal well in Val
D’Agri (VDA, Italy). We choose this area because
of its complexity and particularity. VDA is a
Quaternary extensional basin located in the
Southern Apennines characterized by a complex
tectonic evolution, high seismic hazard and
significant hydrocarbon exploitation. The basin
hosts the largest onshore oilfield in Europe that

produces oil and associated gas from low-
porosity, fractured Cretaceous limestone.

Wastewater associated to hydrocarbon
production is reinjected into the Costa Molina 2
high-rate well (CM2) into an unproductive
marginal portion of the carbonate reservoir at
2890-3096 m depth (b.s.l.). Initial injection tests
were performed from 2 to 12 June 2006 with
variable duration (from 4 to 32 hr) and hourly
injection rate of 38 m3/hr. During the tests a
maximum well-head pressure of 101 bar was
measured. These tests induced a swarm
microseismicity (69 events, ML comprised by 0.3
and 1.8) recorded by a high-performance local
network run by INGV (Mc 0.4, 23 stations) that
constitutes our testing data-set. We investigate
the full moment tensors decomposing them in
Double-Couple (DC), Isotropic (ISO) and
Compensated Linear Vector Dipole (CLVD)
components by using HybridMT technique. We
obtain significant contribution of %ISO and %CLVD
components that tend to increase with time. Also,
we compute the moment magnitudes (that we
compare with ML) and the static stress drops (by
spectral analysis). Finally, we discuss each
analysed source parameter as a function of the
injection pressure curve in the geological/tectonic
contest.