Mozambique: USGS and USAID/OFDA Assessment of

UNCLAS SECTION 01 OF 03 MAPUTO 001032

SIPDIS

SIPDIS

USAID/DCHA/OFDA FOR GMAYBERRY
USAID FOR AA/AFR AND AFR/SA

E.O. 12958: N/A
TAGS: EAID PHUM MZ
SUBJECT: Mozambique: USGS and USAID/OFDA Assessment of
February 23 Earthquake

Ref: Maputo 232

Maputo 241


1. Summary. A magnitude (M) 7.0 earthquake that occurred in
Machaze, Mozambique on February 23, 2006 raised awareness
that a large earthquake could occur in the country.
Detailed analysis of the seismicity in Mozambique is needed
to determine if a large earthquake could occur near highly
populated areas or significant infrastructure such as the
Cahora Bassa dam. The first step in assessing the potential
seismic risk in the country is to strengthen the national
seismic network in order to pinpoint the location of small
earthquakes, which reveal the location of faults that have
the potential for larger earthquakes in the future. A team
composed of the USAID Office of U.S. Foreign Disaster
Assistance (USAID/OFDA) geoscience advisor and seismologists
from the U.S. Geological Survey (USGS) visited the area of
the earthquake and met with key members of the local
geological community to determine what is needed to
strengthen the Mozambique seismic network. They determined
that the highest priority was for upgrading existing seismic
stations, adding seismic monitoring equipment, and training
Direccao Nacional de Geologia (DNG) staff. End summary.

--------------
Overview
--------------


2. A large earthquake occurred in Machaze, Mozambique on
February 23 at 1219 am local time (ref A). According to the
USGS National Earthquake Information Center (NEIC),the
earthquake had a magnitude (M) of 7. Although this was a
large-magnitude earthquake, there was little loss of life
and little damage because the earthquake occurred in an area
with low population density where homes are constructed of
light-weight, flexible materials. If an earthquake of this
size occurred in a highly populated region in Mozambique,
for instance the cities of Beira or Maputo, the impact could
be much greater. The seismic network in Mozambique, which
is used to record and locate earthquakes, is inadequate by
modern standards. It consists of only four stations, three
of which are equipped with obsolete seismographs and have no
telecommunications capability. Accordingly, the seismic
hazard in the country is not well known because the network
cannot locate small earthquakes, which are indicative of
where larger ones could occur.


3. In response to the M 7 earthquake, seismologists from the
USGS, with funding from USAID/OFDA, traveled to Mozambique
to work with the DNG. They evaluated the potential for
large (M greater than 6) earthquakes that could pose a
threat to populated regions or to critical infrastructure
including the Cahora Bassa concrete arch dam on the Zambezi
river. The seismologists found that in-kind support and
funding that DNG had received from other donors met some of
their needs, but there is still a need to 1) upgrade
existing seismic stations, 2) add new stations for better
coverage, and 3) train the staff to operate and maintain the
new systems as well as to analyze complex seismic data.


4. In order to help DNG assess the seismic hazard in
Mozambique, which will help the government and at-risk
communities prepare for large earthquakes, USGS proposes to
cooperate with DNG for a major upgrade of the Mozambique
seismic network. This proposed project will involve
establishing four new stations and upgrading three current
stations so that broad-band, real time data are available.
The future upgraded Mozambique seismic network would consist
of several broad-band stations communicating data in real
time to the DNG headquarters. USGS proposes to provide
technical assistance in site selection, training, and
evaluation of performance. The primary goal of this
proposed effort is to assist the DNG staff in developing an
independent and self-sufficient Seismic-Hazard Reduction
Center in Mozambique that collects and processes regional
seismic data in real time and interprets these data in ways
useful to the mitigation of earthquake effects.


5. With funding from USAID/OFDA, during July 17 through 20
two USGS seismologists and the USAID/OFDA geoscience advisor
travelled to Mozambique. Their goal was to determine what
assistance DNG needs in order to improve their seismic
network so they can eventually issue real time earthquake
notifications and produce a detailed map of the seismic
hazard in the country. The group also evaluated the
potential for large (M greater than 6) earthquakes to pose a
threat to highly populated areas and critical facilities.
While in-country they met with staff from the U.S. embassy

MAPUTO 00001032 002 OF 003


in Maputo, the USAID mission, Direccao Nacional de Geologia,
and the administrator of Chitobe near where the earthquake
occurred. In South Africa, the team met with the Resources
and Science Specialist with the U.S. Consulate in
Johannesburg, the USAID/OFDA Regional Advisor for southern
Africa, and representatives from the USAID office of Food
For Peace, the U.S. Agency for International Development
(USAID),and the UN Office for the Coordination of
Humanitarian Affairs (OCHA).


6. The trip to Mozambique was preceeded by a visit to the
Africa Array workshop in Johannesburg, South Africa, during
July 20 through 21. Attending the workshop allowed the
assessment group to meet with the director of DNG, current
and potential donors to the Mozambique seismic network, and
members of the seismological community from other African
countries who would be able to share seismic data with
Mozambique, futher strengthening their network.

--------------
Geologic setting
--------------


7. The NEIC reported that the February 23rd earthquake
occurred near the southern end of the East African rift
system. The East African rift system is a diffuse zone of
crustal extension that passes through eastern Africa from
Djibouti and Eritrea on the north to Malawi and Mozambique
on the south. The East African rift results from spreading
between the Africa tectonic plate on the west and the
Somalia plate on the east. At the earthquake's latitude,
the Africa and Somalia plates are spreading apart at a rate
of several millimeters per year. The largest earthquake to
have occurred in the rift system since 1900 had a magnitude
of about 7.6. The western branch of this rift terminates in
southern Mozambique, while the eastern branch travels
through Kenya and continues into Tanzania. There is
persistent seismicity within the Mozambique channel,
suggesting that the eastern branch of the rift may continue
into the Indian Ocean, possibly to the southwestern Indian
Ocean ridge.

--------------
Field survey
--------------


8. The M 7 earthquake on February 23rd occurred in Machaze,
the southernmost district in the western province of Manica,
about 215 km (135 miles) SW of the city of Beira,
Mozambique. There were reports of 4 deaths, 36 injuries,
and 1,440 people made homeless. The earthquake was felt as
intensity VI (strong perceived shaking, light potential
damage) in Beira, approximately 215 km (135 miles) northeast
of the location of the earthquake, and intensity IV (light
perceived shaking, no potential damage) in Maputo, about 500
km (310 miles) to the south. Within the epicentral area
(the area near where the earthquake occurred),spectacular
surface faulting was seen, with a crack actually running
through a traditionally built dwelling and one splitting a
tree. Extensive liquefaction was also seen, which is a
process by which water-saturated sediment temporarily loses
strength and acts as a fluid. The maximum surface slip of
about 2 meters was consistent with the large magnitude
measured for this earthquake.


9. The primary natural hazard affecting Mozambique is
flooding, a result of low-lying topography and heavy
rainfall. Earthquakes, in contrast, are thought to be a
much less important source of hazard, largely because the
African continent generally has quite a low level of natural
seismicity. Similarly, the February 23rd Machaze
earthquake, although of considerable magnitude, resulted in
few casualties and severe damage to only a small number of
dwellings considering the size of this earthquake for
several reasons. First, the epicentral region is sparsely
populated. Second, houses in the epicentral area were
largely undamaged because most of these structures are made
of light-weight materials as was reported by seismologists
from Imperial College, England, who conducted a field survey
shortly after the earthquake. In contrast, many of the
structures made of unreinforced brick masonry collapsed to
some extent, resulting in a few fatalities. Third,
earthquakes with associated surface faulting tend to yield
lower levels of damaging ground motion compared to those
involving buried faults (no surface rupture). Fourth,
earthquakes in extensional tectonic environments, including
the East African rift belts where the Machaze earthquake
occurred, show lower levels of damaging ground motion

MAPUTO 00001032 003 OF 003


compared to their counterparts in compressional environments
(e.g. Iran).


10. To date, relatively little attention has been paid to
the potential for seismic hazards in Mozambique, which is
evidenced by the archaic and sparse seismic monitoring
system currently in place in the country. However, the
nature and magnitude of the February 23rd Machaze earthquake
has raised serious questions regarding the hazard associated
with large earthquakes that might occur in densely-populated
regions in Mozambique, or near critical facilities like the
Cahora Bassa concrete arch dam on the Zambezi river. The
Cahora Bassa dam, the 2nd largest in Africa and the 4th
largest in the world, has impounded an enormous reservoir
and generates 2.1 mega-watts of electricity. In the event
of a nearby strong earthquake, the integrity of the dam
might be compromised, resulting perhaps in flooding and loss
of electrical power delivered to Mozambique, South Africa,
and other neighboring countries.


11. Current seismic hazard maps of Mozambique lack detail
and are based largely on expected seismicity associated with
the East African rift. However, it is possible that other
types of faulting could be present, but are not yet
identified from Mozambique's limited earthquake data base.
Such additional sources of seismicity could change the
hazard map to some extent. Currently the seismic network
run by DNG is too sparse to record and locate earthquakes at
a sufficiently low magnitude threshold to determine the
likely sources of damaging ground motion due to future
earthquakes. Currently, data from three of the four
existing seismic stations that DNG runs are periodically
retrieved manually and sent to the Council for Geosciences
in South Africa for analysis, the results of which are then
sent to DNG. This process, which takes at least a month,
precludes the possibility of responding to major damaging
earthquakes in a timely manner, and also compromises the
ability of the DNG to develop a realistic seismic hazard map
based on up-to-date information.

--------------
Future plan
--------------


12. The French embassy in Mozambique and the Council for
Geoscience in South Africa have already provided DNG with
computer equipment and training, respectively. Additionally,
the Intergovernmental Oceanographic Commission (IOC) intends
to establish three stations along the coast of Mozambique as
part of the Indian Ocean tsunami warning network. Based on
the results from the assessment trip and pending funding,
USGS proposes to work with DNG at their request to develop a
new, vastly-upgraded Mozambique seismic network that will
consist of eight stations equipped with state-of-the-art
seismometers, digitizers, and telemetry via cellular
technology.


13. There are four key roles that the USGS plans to play:
(1) definition of network goals and derived products,
including seismic hazard maps, (2) assistance during network
construction and evaluation of performance, (3) equipment
acquisition and installation, and (4) training in network
operations and data processing, ensuring that local
scientists and engineers become independent operators of the
network. The primary end-product of this network will be
the production of an improved probabilistic seismic hazard
map for Mozambique. This map will delineate the zones where
the likelihood of damaging ground motion is the greatest so
that appropriate hazard mitigation activities can be
prioritized and undertaken. Additionally, USGS will advise
DNG in the development of information products to help
educate the public about how to prepare for large
earthquakes and tsunamis.


14. This report was written by members of the USGS and
USAID/OFDA team that visited Mozambique in July.


Dudley