Page 383 - Caldera Volcanism Analysis, Modelling and Response

358 Thomas R. Walter

3.1.2. Deflating spherical magma chamber with a nearby reactivated fault
Caldera systems are often located in tectonic areas already faulted by previous
geological processes. In this set of models, a fault is introduced that is passively
allowed to slip in the along-strike and dip-slip direction. All other model
parameters, magma chamber shape and position, loading and output, are the same
as described in the previous model. The fault is vertical and oriented south to
north, 5 km from the magma chamber (Figure 3A). Displacements are calculated
in map view (Figure 3B) and along cross-section x–xu, perpendicular to the fault
(Figure 3C, D). The pattern of subsidence above the evacuating magma chamber

Deflating spherical magma reservoir nearby reactivated fault

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

Magma chamber
(10 MPa 20
pressure drop)
10
5 X X'
0 Subsidence
Subsidence
Subsidence
-10
Freely slipping
vertical fault -20

-20 -10 0 10 20 -20 -10 0 10 20

C) Cross-section, x-displacement (U )
x
0
X X'
-10

-20

D) Cross-section, z-displacement (U z ) [in m]
0
X X' 1
Freely -10
slipping 0
fault
-20 -1
-20 -10 0 10 20
Figure 3 De£ation of a spherical magma chamber near a reactivated fault. (A) Model setup
(x--y plane). A linear vertical fault is de¢ned 10 km from the magma chamber, from 2 to
20 km depth.The magma chamber is subject to a pressure drop of 10 MPa. As a result, the fault
can be reactivated and slip in dip-slip and strike-slip motion. (B--D) Same as in Figure 2;the
fault is shown only in D. Note that displacement vectors and ¢elds are in£uenced by the fault.