SUNDAY 9 SEPTEMBER, 2018 – UWI TODAY
7
EARTHQUAKE
Prepared by Alia Juman, Education & Outreach, The UWI Seismic Research Centre
Senior Research Fellow and Seismologist at The UWI-
Seismic Research Centre,
Dr. Joan Latchman
answers
some pertinent questions that have arisen since the
event.
How long after an event like this one can we
expect aftershocks and how large can they be?
We can expect aftershocks to continue for weeks and
even extend to years. We cannot estimate how long
the area in which the earthquake occurred will take to
settle and as such aftershocks related to this event can
be recorded and felt over a long period of time. From
past events, we observed aftershocks in the magnitude
5.0 – 5.9 range and this was recorded on Wednesday
22, August at 9.27 a.m. Other aftershocks have been
felt and will continue to be felt over the coming weeks
and months.
This was the longest shaking most persons
have ever experienced (a maximum of 90
seconds was reported) and many people ran
out of buildings during this event. Is this the
safest thing to do?
Generally speaking, no. During an earthquake, it
is best practice to stay where you are. If you are
outdoors, stay there and move away from things
that can fall (e.g. buildings, trees and electricity
wires). If inside, do NOT try to exit the building. It
may seem unsafe to stay in a shaking building, but,
research has shown that most casualties are caused by
falling debris as persons run to seek ‘safer’ areas. We
recommend you Drop, Cover and Hold on (DCH)
until the shaking stops. Stay away from windows and
unfixed objects. We do not recommend going under
doorways as construction methods have changed. If
there is no sturdy piece of furniture, you still drop and
cover your head and neck, remaining alert at all times.
Conducting regular earthquake drills can serve to
encourage persons to adopt this safety technique.
You have been quoted numerous times about
the need for T&T to be prepared for a large
earthquake. Was this it?
This earthquake was not in the range that we consider
the event that the region can experience. The region
has experienced events close to magnitude 8 and these
are the ones, for which we have warned the public
to be prepared. This one was not the strongest but
it serves to reinforce the fact that large earthquakes
can and will occur. The duration of shaking and the
damage that occurred during this event highlighted
what still needs to be done to better be prepared for
larger events. Such events need not be the largest
possible but can simply be sufficient to cause damage.
This was
not
the Big One
Seismologist says more to come
The Eastern Caribbean region is susceptible
to large earthquakes and Trinidad and Tobago is no exception. Scientists, researchers, disaster officials
and others have echoed this statement for decades but the public often responds to felt events with some alarm and calls for action that are usually
quickly forgotten. On Tuesday 21, August, 2018, the largest earthquake event in the last 50 years brought earthquakes; their associated dangers and our
island’s vulnerability back to the front pages and to the forefront of the nation’s discussions. The magnitude 6.9 event was located west of Trinidad at a
depth of 127 km and was felt as far north as Dominica, as far west as Colombia and as far south as Suriname. Intense ground shaking, structural damage
and liquefaction were observed and in the aftermath, disruption of the mobile networks, electricity and water supplies was experienced. Despite the
large magnitude, no casualties or fatalities were reported, in Trinidad and Tobago. The largest aftershock, at magnitude 5.9, was recorded just under 14
hours later. Up to 10 a.m. on 23 August, 37 aftershocks were recorded.
The magnitude of this event was almost to the
same as the 2010 Haiti event. Why is there not as
much damage?
The 2010 Haiti event was located at a very shallow depth,
close to a densely populated area with poorly constructed
buildings. As a result, more energy reached the surface
and more damage occurred. Had the 6.9 event been
shallower and closer to Trinidad, we would have seen
much more damage.
When the earthquake occurred, there were various
magnitudes being reported. Which one is correct
and why can all the agencies not use the same
method?
Different monitoring agencies use different systems for
determining magnitude given their location and their
network. As such there are different types of reported
magnitudes, with different values. This apparent
discrepancy is, therefore, expected and acceptable to
scientists with each agency’s value being correct in its
own context.
Established in 1953, the
Seismic Research Centre
is an agency within The UWI. The UWI
Seismic Research Centre is the leading authority on earthquake and volcanic activity in the
English-speaking Eastern Caribbean. It operates the largest network of seismographs and
other geophysical instruments in the Caribbean region, manages the Montserrat Volcano
Observatory and conducts education and outreach activities in these countries. The Centre
is involved in a regional effort to establish a tsunami warning system for the Caribbean.
For more information, please visit
Why was a tsunami warning issued if no tsunami
waves were observed?
A tsunami warning was issued by the Pacific Tsunami
Warning Center (PTWC); the agency that monitors
tsunamis for the region. This is part of the normal
procedure for an earthquake of this magnitude. The
warning does not necessarily mean that tsunami waves
have been generated from the event. An advisory was sent
out shortly after determining that no tsunami waves were
observed and the warning cancelled as per procedure.
Industrialized countries like the US and
Japan have some warning system in place for
earthquakes. Earthquakes cannot be predicted,
but why can we not have something like that here?
The warning systems that industrialized countries may
have for earthquakes give only a few seconds’ notice
before large events, which they have tried to use to send
out warning messages and are usually linked to critical
facilities such as power generation plants and hospitals.
This allows these critical facilities to shut down operations
just before the ground shaking starts preventing further
damage to costly and critical machinery. In 2015, research
was conducted to determine the usefulness of such a
system in the Eastern Caribbean, with various regional
stakeholders from critical facilities participating. It was
found that the relatively short distances involved, in this
region, would afford only a very short warning time,
which had very limited application to us.
Has there been an increase in global seismic
activity in recent years and is this event linked to
it? Can we expect more and stronger earthquakes
in the coming months?
The global seismic system has been steadily producing
more large magnitude events since the mid-1990s,
reflected in the mega-earthquakes occurring around the
world, since 2004. This earthquake fits with expected
activity for the Eastern Caribbean, although the global
system had a shortfall in 2017, which seems to have
continued into 2018. Of course, there are still several
months to go in 2018 and time will tell if the shortfall
continues.
Dr. Joan Latchman
