Geology Reference
In-Depth Information
Fig. 9.19
Unfiltered vertical, radial, and transverse
components of ground velocity, recorded at station
IRIS/ANTO (Ankara, Turkey), for an earthquake with
epicenter in Crete,
Mw
6.7, which occurred on October 12,
2013 h13:11:52.4000. Epicentral distance is
D
8.72
ı
Fig. 9.20
The same seismogram of Fig.
9.19
after application of a Wood-Anderson simulation filter.
S
wave arrival on
the vertical trace is enhanced by this operation
illustrated in Fig.
9.20
. Both these seismograms
have been analyzed using
SeisGram2K
, a public-
domain software tool for the visualization
of seismic traces designed by Antony Lo-
max
(
http://alomax.free.fr/software.html
)
. The
nomenclature of seismic phases in the near field
includes both
crustal phases
and
surface waves
(Fig.
9.21
).
The first arrival of
P
waves in the near field
is either a
Pg
or
Pn
phase. A
Pg
phase is a
P
wave having its turning point in the crust, while
a
Pn
phase is a low-amplitude phase associated
with a refracted wave, generated at sub-critical
incidence angle and travelling almost horizon-
tally just below the Moho. Finally, a reflection
from the Moho discontinuity is called a
PmP
