THE EFFECTS OF FEBRUARY 3rd, 2008
EARTHQUAKE IN THE LAKE KIVU BASIN,
WESTERN RIFT VALLEY
Wafula MIFUNDU1, Byamungu MATABARO1, Ciraba MATESO2, Mukambilwa
KIBUYE2 , Ciza ASSANI2 , Kasereka MAHINDA2, Cinyabuguma KASISI2 Hamaguchi
HIROYUKI3, Kasahara MINORU4, Maeda TAKAHIRO5, Zana NDONTONI6
and Moshi MVULA6
ABSTRACTThe lake Kivu basin had experienced an earthquake of local magnitude ml= 6.1 on February 3rd, 2008
at 7h34’ UT, in its south-western part. Many phenomena were generated in the lake Kivu and on the
shorelines. At several places were observed land subsidence on the shoreline where several children
were killed in D.R. Congo and Rwanda sides. At other places land uplift was observed. According to
the fishermen, small tsunami was generated and attacked the coast lines. The highest level accessed by
the tsunami was estimated to 4m at Ibindja Island. The small gas escaping generated by the tsunami
was observed at several places in the lake Kivu. Many damages were recorded in Bukavu city andsurrounding areas in D.R. Congo and Rwanda, characterized by the fissures on the walls or collapse ofhouses. Total 49 people were killed by the earthquake and aftershocks, more precisely 10 in D.R.C.
and 39 in Rwanda. This event was preceded by many foreshocks and followed by a long duration offelt aftershocks. The focal mechanism of this event indicates a normal fault. The maximum intensity
was recorded close to the epicentre area and estimated to VIII-IX.

1

Department of Geophysics, CRSN, D.R. Congo
Goma Volcano Observatory, Department of Geophysics, CRSN, D.R. Congo
3
Faculty of Science, Tohoku University, Sendai, Japan
4
Institute of Seismology and Volcanology, Graduate School of Science, Hokkaido University, Japan
5
National Research Institute for Earth Science and Disaster Prevention, Japan
6
Centre de Recherche Géophysique de Kinshasa, D.R. Congo
2

Wafula MIFUNDU <dmwafula@yahoo.fr>
Byamungu MATABARO <david_byamungu@yahoo.fr>
Ciraba MATESO <honoreciraba@yahoo.fr>
Mukambilwa KIBUYE <kmuka1@yahoo.fr>
Ciza ASSANI <delphinassani@yahoo.fr>
Kasereka MAHINDA <mkaseraka@yahoo.fr>
Cinyabuguma KASISI <mcinyabuguma@yahoo.fr>
Hamaguchi HIROYUKI <hamaguti@cello.ocn.ne.jp>
Kasahara MINORU <mkmikeno@yahoo.co.jp>
Maeda TAKAHIRO < tmaeda@bosai.go.jp>
Zana NDONTONI <azanan2002@yahoo.fr>
Moshi MVULA <fremoshi@yahoo.fr>

INTRODUCTION
The East African Rifts system extends from the Red Sea and Gulf of Aden at Afar triangle, Ethiopia in
the north to Mozambique in the south, and divided into two branches; the Eastern and the Western
which come across at the lake Malawi (Figure 1). The Western branch also called Western Rift Valleyof Africa includes six lakes; namely: Albert (619 m), Edward (912 m), Kivu (1462 m), Tanganyika(771 m), Rukwa (782 m) and Nyasa (472 m) (Malawi).
The Western Rift Valley is seismically very active region in the East African Rift System.
Both the East African Rift System and the mid-oceanic ridge are characterized by the seismic activity
confined to shallow depths. However, the seismic belt within which earthquakes occur is narrow underthe mid-oceanic ridges, while it is rather broad in the African Rifts (Tanaka et al. 1980).
The different seismic studies on the Western Branch of the East African Rifts System revealthat the seismic activity is confined in the following regions:-the region of the lakes Malawi and Rukwa;
the region of the lakes Moero and Upemba;
the South-Eastern, the Central and Northern border of the lake Tanganyika;
the Ruzizi plain;
the lake Kivu basin, including the Ngweshe, Masisi and Walikale regions,the lake Edward region;
the Mt. Ruwenzori region;
the lake Albert region ;the South Sudan region.

Fig.1 The East African Rifts System (Hamaguchi and Zana, 1983a).

The lake Kivu basin in this paper includes the Ngweshe, Masisi and Walikale regions. This
lake is the highest lake in the Western Rift Valley, implying that the center of doming accompanying
the Rift formation must be located around this lake (Hamaguchi and Zana 1990). The tectonic
conditions of the dome uplift, faulting, volcanism and shallow seismicity around the lake Kivu are
believed to be the indications of actual rifting and may represent a nascent stage in the development ofplate boundary (Wong and Von Herzen 1974).
In the Kivu lake basin, the faults of the rift are concentrated in netting following three main
directions NE-SW, N-S and NW-SE (Figure 2).
The result obtained from December 1979 to December 1980 had shown an importantconcentration in the basin (Zana et al. 1989) (Figure 3). The seismic activity is mostly concentrated in
the South-Western part of the basin with extension to adjacent regions of the rift margin the Masisi
and Walikale.

Fig.2 Geological structure of lake Kivu. Open circles represent Earthquake epicentres, lines represent
fault and areas of enozoic volcanics are shaded (Wong and Von Hen 1974, modified).

Fig.3 Seismicity of lake Kivu basin December 1979 December 1980
Solid circle: earthquakes (modified)
Since 1997, the lake Kivu basin has been experiencing an unusual high seismic activity; many
earthquakes are felt by local inhabitants. On October 24, 2002 an earthquake of magnitude Mw= 6.2
had struck the Region. This event generated damages on buildings, land subsiding at some place on
the lake Kivu shore, and took the life of 8 people. Many aftershocks followed this main event.
In regard to the earthquake mechanism, it is noticed that the focal mechanism of normal
faulting type prevails widely in the Western Rift Valley with the tension axis approximately
perpendicular to the strike of the East African Rift System as a whole or the local fault trends in detail(Zana and Tanaka, 1981, and Wafula and Zana, 1990).
This paper focuses on the effects and associated phenomena to the recent earthquake which
struck the Lake Kivu basin on February 3rd, 2008.

METHODS AND MATERIALSThe seismic activity in the lake Kivu basin is recently studied using the Lwiro station located on thewestern part of the lake Kivu, constructed since 1953 by CRSN/ Lwiro, previously IRSAC and IRS.
The station was equipped with the Benioff short period seismographs (To= 1sec, Tg=0,25 sec, Mag=
ca.100k). Recently, Lwiro station is equipped with a short period Kinemetrics vertical component SS1 ranger seismometer (To=1s) connected to PS-2 seismic recorder.
To the Lwiro station is added since 1983 a seismic network constructed in the northern end oflake in the Virunga volcanic region. The seismic stations are distributed around the active volcanoes
Nyiragongo and Nyamulagira. Recently all stations are using the same equipment than the Lwiro
station which is inemetrics.
In May, 2004 a new telemeter network was installed using the same stations. The signals fromthese stations (three components; one horizontal and two vertical) are locally digitized from a datalogger with sampling frequency of 50 Hz and an A/D resolution of 24 bits, and telemeter to Gomabase station where they are recorded in triggered and continuous files. Actually the seismic network in
the Virunga region is shown in Figure 4.
Geophysical observations were carried out around the lake Kivu basin to evaluate the damages
caused by the main shock and aftershocks. During the field observations the temporary seismic
stations were installed around Lwiro located about 10 km from the epicentre area and the GPS wereused to determine the geographical coordinate of investigate areas.

Fig.4 Seismic network around the volcanoes Nyiragongo and Nyamuragirain the Virunga region Circles and crosses indicate the analog seismic
stations and squares and crosses indicate the telemeter seismic stations

RESULTS
The results obtained from our observations are presented in two subheadings.
Seismicity
The earthquake which struck the lake Kivu basin on February 3rd, 2008 at 7h34’ UT had a magnitude
mb= 6.0. The event occurred on the western part of the lake Kivu at latitude 2.30 °S and longitude
28.90 °E at 10km depth. One foreshock considered as precursor of this event was recorded on
September 07th, 2007 with magnitude mb= 4.6. Many aftershocks followed this main event for longtime (Figure 5).

Fig. 5a Number of earthquakes recorded at Lwiro station, February to August 2008

Fig. 5b Number of earthquakes recorded at Rusayu station, February to September 2008

Many aftershocks were strongly felt such as: the February 3rd, 2008 at 10h56 UT withmagnitude 5.10 mb at latitude 2.40°S and longitude 28.97°E at 10km depth, the February 14th, 2008
with magnitude mb= 5.4 at 02h07 UT latitude 2.39°S and longitude 28.88°E at 10km which was themain aftershock, and the last strongly felt earthquake recorded on June 8, 2008 with magnitude mb=
5.0, about for month late. It was clearly observed that the aftershocks were felt up to June 2008 in
Bukavu city and surrounding areas. The seismic activity of lake Kivu basin for earthquakes withmagnitude ≥ 4.0 for the period from 1970 to 2008 is shown in Figure 6a.

Fig.6a The seismicity of lake Kivu basin for earthquakes withmagnitude ≥ 4.0, for the period from 1960 to 2008
(Solid circles: earthquakes; Blue solid circles: aftershocks associated to the October 24,
2002 earthquake, encircled red solid circle; Green solid circles: aftershocks associated to
the February 3rd, 2008 earthquake represented by solid circle with clear green color.)

The epicentre distribution of aftershocks associated to the February 3rd, 2008 and earthquake
in Birava for the period from April 28 to May 27, 2008, are shown in Figure 6b.

Fig. 6b Epicenters of aftershocks associated to the February 3rd, 2008,
earthquake for the period from April 28 to May 27, 2008

T
The geologyy of Katana sectors
was sttudied by Viilleneuve (19983) Figure 77. In this secctor threemain dirrections of faaults are NE-SW, NW-S
SE and NEE--SWW are seeen. The Kakkondo-Birav
va fault isbelievedd to be the moost impressiv
ve and the mmost active ob
bserved.
Field obbservations
M
Many phenoomena were generatedg
insside the lake and on the shoreline. At several placces wasobservedd land subsidding on the shhoreline. Fivve children were
w killed, tw
wo at Ibindjaa island in D.R.
Congo side (Figure 8a)
8 and threee at Nkombo island in Rw
wanda side (FFigure 8b).

Fig. 7 Geeology of Kaatana sector.

Figg. 8a Land suubsiding on thet shorelinee
at Ibindjaa island (©W
Wafula)nd subsidingg on the shore line
Fig. 8b Lanat Nk
kombo islandd. (©Wafula))

The two islands Ibindja and Nkombo are close to the epicenter area. At other places land uplift
was observed. According to the fishermen; small tsunami was generated and attacked the coast line.
The highest level accessed by the tsunami was estimated to 4m at Ibindja island. The small gas
escaping generated by the tsunami was observed at several places in the lake Kivu.
Many damages were recorded in Bukavu city and surrounding areas in D.R.C. and Rwanda,
characterized by the fissures on the walls or collapse of houses Figure 9. Fissures were observed also
on the soil with directions approximately 320ºN (N-S) and others N60º (E-W). At the crossing point ofthese two directions the damages were more important on the walls of houses. These observations
have been made in the Bukavu region as to Rwanda.

Fig. 9a Collapsed house with three floors,
Bukavu city (Feb. 7, 2008) (©Wafula)Fig. 9b Collapsed house with two floors,
Bukavu city (Feb. 7, 2008) (©Wafula)Fig. 9c Collapsed house at Bushenge hospital(Rwanda) (Feb.19, 2008) (©Wafula)At the epicentre area Birava, it was noticed the total collapse of the chimneys of house Figure
10. The fissures observed on the wall were very diversify, some were vertical and very wide (Figure11a), and some others complex. (Figure 11b) Total 49 people were killed by the earthquake andaftershocks, more precisely 10 in D.R.C. and 39 in Rwanda. The latest aftershock with magnitude
greater than 5.0 was felt on June 8, 2008, 4 months after and killed one people. The main fault was in
the direction approximately N-S (N320º) according to the magnitude of the main shock its length wasestimated to about 10 km.

Fig. 10 The collapse of the chimney of house at Birava (the closest town to the epicentre area)
Apr. 19, 2008 (©Wafula)Fig.11a Wide vertical fissures observed on thewall at Kankule (D.R.C.), Apr. 28, 2008,(©Wafula)

Fig.11b Complex fissures on the Wallat Bukavu, Feb.18, 2008,(©Wafula)Fig.12 Intensity distribution of February 3rd 2002 earthquake at Birava.
The maximum intensity recorded was VIII-IX at Ibindja and Nkombo islands in Figure 12.
CONCLUSIONS
Since 1997, the lake Kivu developed a high seismic activity. Two earthquakes with magnitude morethan 6.0 already occurred in the basin. The earthquake on February 3rd was the most destructive event
because it occurred near the big city of Bukavu.
Total 49 people were killed by the earthquake and aftershocks, more precisely 10 in D.R.C.
and 39 in Rwanda. This event was preceded by many foreshocks and followed by a long duration offelt aftershocks.

During the earthquake small tsunamis occurred. This fact is confirmed by the lake Kivu water
which arisen the cost line at Ibindja island up to 4 meters and the occurrence of bubbles observed in
the water as tested by the people staying on the cost lines during the earthquake.
In the lake Kivu is concentrated a huge amount of carbon dioxide and methane gases
dissolved in the water and keeping a stable condition. In case the earthquake generated a big tsunamis
in the water of lake Kivu, it may be possible to assist to the phenomena of explosion of gases that may
be the most fatal catastrophe for which scientists should pay much attention.
The maximum intensity recorded was VIII-IX at Ibindja and Nkombo islands. These twoislands were the most affected area the earthquake.
According to the recent seismic activity developed in the lake Kivu basin it is rather toconclude that this region remains among the most seismically active region in the Western Rift Valley,
so the resilient structure should be performed for buildings, dams, bridges, to avoid any surprises that
may stop the development around the lake Kivu basin. In case of Bukavu city and surrounding areas itis necessary to limit the uncontrolled construction on unstable terrain such as steep slopes, the edge ofLake Kivu.
ACKNOWLEDGMENT
We are very grateful to the Rwanda Red-Cross members for their assistances during our fieldobservations in Rwanda. We are also grateful to Birava and Kabare catholic churches for offering us
spaces to install our seismic stations. We would like to extend our thanks to all staff of Geophysics
Department of CRSN/ Lwiro.
REFERENCES
Hamaguchi, H. and N. Zana, 1983a, Introduction to the volcanoes Nyiragongo and Nyamulagira. In:
Hamaguchi (Ed.), volcanoes Nyiragongo and Nyamulagira, Geophysical Aspects, Fac. Sci.
Tohoku Univ. Sendai, Japan, 1-6.
Hamaguchi, H. and N. Zana, 1990, A Great Circle Distribution of four Active Hotspots: Evidence for
Deep Mantle Plumes. Tôhoku Geophys. Journ. (Sci. Rep. Tôhoku Uni. Ser. 5), Vol. 33,
Nos. 3, 4, 251- 262.
Tanaka, K., S. Horiuchi, T. Sato., and N. Zana, 1980, The earthquakes generating stresses in theWestern Rift Valley of Africa , J. Phys. Earth, 28, 45-57.
Villeneuve, M., (1983), Les formations précambriennes de Katana au Kivu oriental (Zaïre), Mus.
Roy. Afr. Centre., Tervuren (Belg), Dépt. Géol. Min., Rapp. Ann. 1981-1982, 153-159.
Wafula M., and N. Zana, 1990, Focal mechanism study of earthquakes in the Western Rift Zone
and Central Basin of Zaire. Rev. Sci. Nat. Vol. 1 No. 1, 75-92.
Wong H.-K., and Von Herzen R.P., 1974, A geophysical Study of Lake Kivu, East Africa, Geophys.
J. R. Astron. Soc., 37, 371-389.
Zana,N., and K.Tanaka,1981, Focal mechanism of major earthquakes in the Western Valley of Africa,
Tôhoku Geophys. Journ. (Sci. Rep. Tohôku Univ. Ser. 5), Vol 28, Nos 3-4, 119-129.
Zana, N, M.Kamba, S.S. Katsongo, and Janssen Th., 1989, Recent seismic activity of theKivu Province, Western Rift Valley of Africa. Physics of the Earth and Planetary Interior,
Elsevier Science Publishers B.V. Amesterdam, 58, 52-60.