Page 388 - Caldera Volcanism Analysis, Modelling and Response

Facilitating Dike Intrusions into Ring-Faults 363

Deflating sill-shaped magma reservoir, opening at ring-fault

A) Map view, model setup B) Map view, displacement vectors

Magma chamber 20
(10 MPa
pressure drop)
10

0 Subsidence
Subsidence
Subsidence
5 km
y
Opening -10
ring-fault
x -20
-20 -10 0 10 20 -20 -10 0 10 20

C) Side views on opening ring-fault
z z
x y
0

Dike Dike
Amount of
opening [m]
Opening -10
1

0
-4 0 4 -4 0 4
Magma chamber
Figure 6 De£ation of a sill-shaped magma chamber causes opening at a circumferential ring-
fault.The magma chamber is vertically £attened (5 km radius in x and y directions, 2.5 km in
z direction, aspect ratio 2:1), emplaced at (x, y) coordinates (0,0) at 10 km depth, and is subject
to a pressure drop of 10 MPa. All other parameters and sub¢gure explanations (A--C) are the
same as in Figure 5.This model suggests that the zone of maximum opening is restricted to very
close to the sill-shaped magma chamber.The pattern is radially symmetric, so dike intrusion
(shown by black arrow) may occur as a complete ring.

3.3. How processes external to the caldera system may affect the
location of ring-dike intrusions

3.3.1. Tectonic earthquake at a distance
Many calderas systems are located in highly active tectonic regions where large
earthquakes can occur and affect the activity of the volcano magma system. In this