At 4 :20 AM on August 2, 1968, a major
earthquake, the most powerful of a
series to shock the country in at least
two decades, jarred Northern Luzon and
battered some sectors of Manila. The
sudden sharp strain caused the
six-storey Ruby Tower Apartments in Sta.
Cruz District to collapse resulting in
the death of more than 300 persons.
Several other structures sustained
damages which amounted to millions of
A few days after that major tremor,
there were reported in the metropolitan
newspapers the existence of two
faultlines, each approximately 15 kms.
long, traversing the Manila area in a
northwesterly direction. One fault, as
reported, extends from Manila Bay
cutting through the intersection of
Herran Street and Taft Avenue and
continues to the Marikina Valley passing
through Guadalupe in Makati (Fig. 1).
The other fault, reportedly passing
directly under the
Ruby Tower Apartments possibly causing
its collapse, runs from Manila Bay
through Tutuban Station at Claro M.
Recto Street and, likewise, extends to
Marikina Valley passing through the
northern approach of the Guadalupe
Bridge in Makati. Further, as reported,
these faults bound a postulated graben.
As a form of public service and for
geological information, the Board of
Directors of the Geological Society of
the Philippines formed an AD HOC
Committeei to make a review of the
geology of the Greater Manila area to
verify such reports.