Archaeoseismology and Palaeoseismology in the Alpine ... - Tierra

point was about 80 cm along the shoreline edge with
discernable vertical displacement. Some en echelon
faults in the deeper portion of the bay about 200 m
from the shore were likewise reported by local
fishermen.
Fig. 4: Photograph (looking WSW) showing the ground rupture
produced along the coastline in Suba, Dimasalang. Note the
shoreline that was displaced approximately by 0.8m and the
subtle uplift/mound in the foreground of the photo
About 25 m from the shore, the trace can be followed
along the N48 o W trending fault transecting the sandy
beach berm. In the beach terrace, the fault also
transected two semi‐concrete houses and numerous
wooden fences. The wooden fence was displaced
horizontally and vertically (northwest block up) by
20cm and 18cm, respectively
‐ Palanas area
In Sta. Cruz, Palanas, the ground rupture also displaced
several man‐made structures including semi‐concrete
to concrete houses, wooden fences, rice paddy dikes
and roads and foot trails. Inside one of the gardens, a
displaced foot trail (20 cm horizontal displacement)
was observed with well‐formed mole track. Moreover,
a semi‐concrete house and a wooden house in the
same village were transected by the fault.
Southwards and into Nabangig, Palanas in Sitio
Matugnaw, a foot trail was transected by the ground
rupture. The trail was horizontally displaced by 45 cm
with negligible vertical displacement (site r in Fig. 3). In
this area, the en echelon faults have a N60 o W trend
while the ground rupture is trending N40 o W and about
10 cm wide. Across the creek, a small hill is transected
by the ground rupture wherein the fault trace is well
manifested by right‐stepping en echelon fractures and
mole tracks with an average length of 150 cm (Fig. 5)
located between sites r and s in Fig. 3. Fig. 5 also shows
a coconut tree that was transected by one of the en
echelon. It was noted that the surrounding
geomorphology in Matugnaw area is indicative of a
fault saddle. However, since there was no manmade or
cultural structure transected, there was no horizontal
measurement obtained.
‐ Cataingan area
Throughout the valley and up to the ridge between
Sitio Bogtong and Sito Salag, Pawican of Cataingan
municipality, the trace was also observed right‐
stepping tensional gashes. In Sitio Salag, the trace
approaches the upstream area of Nabangig River. The
1 st INQUA‐IGCP‐567 International Workshop on Earthquake Archaeology and Palaeoseismology
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Nabangig River has a very deep gulley and thick
vegetation preventing the team to investigate the river
vicinities. After crossing the Nabangig River, the trace
was found along a pre‐existing scarp approximately
150cm high. A fault outcrop was likewise found along
the riverbank of Nabangig River.
The fault trace was found again across the asphalt
national highway in Gahit, Cataingan about 1km south
of Gahit Bridge. Interestingly, this trace widened and
became more evident after several weeks. During
initial investigation on February 19 th , 2003, the surface
rupture in this area was just a hairline crack. However,
after two weeks the fissure in this road have widened
to about 0.8cm along an EW direction with differential
horizontal displacement of about 3cm. Moreover, the
en echelons became more and apparent along the
asphalt road.
Fig. 5: The ground rupture in Matugnaw, Palanas manifested
as mole tracks and tensional gashes on grass‐covered hill also
cutting through the coconut tree.
‐ Bogtong Island
Based on the projection of the trace from San Pedro,
Cataingan municipality, the Island of Bogtong (Fig. 1)
was likewise investigated to check the effects of the
February 2003 earthquake and the possibility that the
ground rupture transects the island.
There was no clear indication of any presence of a
fresh ground rupture based on the investigation and
accounts by the residents. However, in the eastern side
of the island, the limestone hill has a linear flat area.
This feature is most probably a fault scarp considering
the trend and location of the trace of PFZ in Masbate
Island.