Page 390 - Caldera Volcanism Analysis, Modelling and Response

Facilitating Dike Intrusions into Ring-Faults 365

Tectonic earthquake at distance to ring-fault

A) Side view, model setup
Ring-fault
Subduction fault

15 km
5 m slip
100 km

B) Map view, displacement vectors C) Side views on opening ring-fault
z z
20 x 0 y
Fault slip at 100 km distance y Opening -10 -10 Opening Amount of
Subsidence
10
Dike
0
opening [m]
Opening
Opening
0.1
ing f
ault
ring fault
r ring-fault
-20 -10 x 0 10 20 -20 -4 0 4 -4 0 4 0
Figure 8 Remote tectonic deformation acting on a ring-fault. (A) Model setup (x--z plane).
An earthquake was simulated 100 km from the ring-fault, its characteristics resembling a
subduction earthquake. A ring-fault is de¢ned with a radius of 5 km at 0--20 km depth.
Boundary conditions are set so that the ring-fault is allowed to open due to the earthquake.
(B) A map view of horizontal displacement vectors at the surface (x--y plane) shows displace-
ment of the hanging wall toward the earthquake source. Note small subsidence caused by
reactivation of the ring-fault. (C) Side views on opening ring-fault (left showing x--z plane,
right showing y--z plane). Maximum opening occurs at two regions of the ring-fault.
Dike intrusions into the ring-fault are encouraged perpendicular to the slip direction of the
earthquake (potential dike paths shown by black arrow). A similar displacement pattern is
expected for ring-faults subject to rifting episodes.

more on the side closer to the earthquake (Figure 8C). The model thus suggests
that a dike intrusion is encouraged in these two zones, while complete ring-fault
reactivation and ring-dike formation appears unlikely. A similar effect can be
expected for zones subject to tectonic rifting. The models imply that tectonic
deformation may have a large effect on the ring-dike intrusion pattern and thus also
affect the location of an eruption.

3.3.2. Radial dike intrusion outside the ring-fault
Some systems are known for a pattern of radial dikes and fractures outside the
caldera basin (e.g., Galapagos Islands, Chadwick and Howard, 1991; Gran Canaria,