Earthquakes - Extreme Events: A Physical Reconstruction and Risk Assessment - page 171

show that the structure experienced horizontal forces from an earthquake that
post-dated the construction of the temple around 530 BC (Stiros, 1996).

Tree-ring records (dendroseismology) and forest disturbance

Tree rings can record past earthquakes via a number of processes. One
of these includes the survival of trees following seismically induced landslides.
Surviving trees suffer damage such as toppling, tilting, trunk impact or root
breakage and these impacts are recorded in the growth rings of the affected
trees. The oldest undisturbed tree on a landslide provides a minimum age of
the event. Along with landslides, the annual rings in disturbed trees can also
be analysed to date recurrent landslide movements and to determine the mag-
nitude and frequency of debris flows. Some of these methods have been used to
investigate the possible relationship between landslide movements and regional
seismicity in the Gravelly Range in southwestern Montana, USA (Carrera and
O'Neill, 2002).
Trees can also show indirect responses to large earthquakes due to environ-
mental changes. Sheppard and Jacoby (1989)noted that trees died from flooding
caused by a general topographic reversal during the AD 1811--1812 New Madrid,
USA earthquakes. Stands of undamaged trees experience increased growth when
located near to areas of earthquake damaged trees because of the favourable light
conditions after felling of the damaged trees. Trees also respond with increased
growth in areas where coseismic uplifting has moved a shoreline away from a
zone that was previously impacted on occasions by waves that inhibited growth
of those trees. Their new position in the landscape affords them less exposure
to wind, salt spray and root-zone erosion (Sheppard and Jacoby, 1989).
There are three common distinguishing features in tree rings that can be
used to indicate past earthquakes. These are:

(1) an abrupt reduction in annual ring width;

(2) theformation of reaction wood; and

(3) scars.

Disturbances found in the tree-ring record in a specific year indicate that the
disturbance took place between the end of the previous growing season and the
growing season of that specific year. A reduction in annual ring width for several
years or more can be the result of injury due to a geomorphic event such as
an earthquake-induced landslide or avalanche. Damage to the root system, loss
of a major limb or toppling can also result in an abrupt reduction in annual
ring width. When investigating the effects of the AD 1959 Hebgen Lake, USA
earthquake on Douglas firs growing along the fault scarp, 13 of the 15 trees