Piercement structures such as hydrothermal vent complexes, pockmarks,
and mud volcanoes, are found in various geological settings but are
often associated with faults or other fluid-focussing features. This
article aims to investigate and understand the mechanisms responsible
for the formation of piercement structures in sedimentary basins and the
role of strike-slip faulting as a triggering mechanism for fluidization.
For this purpose four different approaches were combined: fieldwork,
analogue experiments, and mathematical modeling for brittle and ductile
rheologies. The results of this study may be applied to several
geological settings, including the newly formed Lusi mud volcano in
Indonesia (Mazzini et al., 2007).
Lusi became active the 29th of May 2006 on the Java Island. Debates on
the trigger of the eruption rose immediately. Was Lusi triggered by the
reactivation of a fault after a strong earthquake that occurred two days
earlier? Or did a neighbouring exploration borehole induce a massive
blow-out? Field observations reveal that the Watukosek fault crossing
the Lusi mud volcano was reactivated after the 27th of May 2006
earthquake. Ongoing monitoring shows that the frequent seismicity
periodically reactivates this fault with synchronous peaks of flow rates
from the crater. Our integrated study demonstrates that the critical
fluid pressure required to induce sediment deformation and fluidization
is dramatically reduced when strike-slip faulting is active. The
proposed shear-induced fluidization mechanism explains why piercement
structures such as mud volcanoes are often located along fault zones.
Our results support a scenario where the strike-slip movement of the
Watukosek fault triggered the Lusi eruption and synchronous seep
activity witnessed at other mud volcanoes along the same fault. The
possibility that the drilling contributed to trigger the eruption cannot
be excluded. However, so far, no univocal data support the drilling
hypothesis, and a blow-out scenario can neither explain the dramatic
changes that affected the plumbing system of numerous seep systems on
Java after the 27-05-2006 earthquake. To date (i.e. April 2008) Lusi is
still active. (C) 2009 Elsevier Ltd. All rights reserved.