EERI Special Earthquake Report — May 2004

Learning from Earthquakes

Preliminary Observations on the Al Hoceima, Morocco,
Earthquake of February 24, 2004
Following the earthquake, Ahmed F.
Chraibi, Ingema, Inc., Rabat, Morocco, accompanied by EERI Member
T. Leslie Youd, traveled to the epicentral area to investigate the damage. The investigators visited thecity of Imzouren, the locality of themost severe building damage andthe most casualties, and investigated the Mohamed Ben Abdelkrim
El Khattabi Dam and the Joumoua
Dam (conducted independently byAhmed Chraibi). This brief report
also contains observations of building damage and information gleaned
from news reports and several websites.
The publication of this report is supported by EERI’s Learning fromEarthquakes Program under National Science Foundation grant # CMS0131895.

Introduction
On February 24, 2004, at 02:27:48
UTC (also the local time), an earthquake of moment magnitude Mw
6.4 (USGS) struck north central
Morocco near the Mediterranean
Sea (epicentral coordinates are
35.235 N, 3.963 W). The epicenter
was about 3.5 km southwest of theundamaged coastal city of Al Hoceima, about 14 km northwest of themost damaged city of Imzouren, andabout 320 km northeast of the capital city of Rabat. The focal depth
was 12.6 km (USGS). The earthquake was felt at distances as greatas 200 km from the epicenter. As ofMarch 8, 2004, 622 casualties werereported.

Figure 1. Location andrapid moment tensor
solution for earthquake(USGS).

under the Mediterranean Sea to thenortheast. The area also lies within
the North Atlas fault zone, which
trends northeastward across Morocco to the epicentral region.
The general location and moment
tensor solution (USGS) for theearthquake is plotted in Figure 1.
This solution indicates that theearthquake was generated by strike-slip motion along either
a north-northeast trending left-lateral fault or awest-northwest trending
right-lateral fault. The
nearest strong-motion
instrument to the epicenter was located near
the right abutment of
the El Khattabi Dam, 21
km southeast of theepicenter. A peak horizontal acceleration of
0.25 g was recordedby that instrument. Strong groundmotion at the dam had a duration of
9 s and high frequencies with a predominant frequency of about 4 Hz.

Mohamed Ben Abdelkrim
El Khattabi Dam
The El Khattabi Dam is one of themajor engineered structures in theepicentral area. It is 27.5-m highSeismicity
The affected region is very seismically active, with hundreds of small
earthquakes in the past 20 years

Figure 2. Post-earthquake view of the El Khattabi dam from right abutment (near thestrong-motion instrument) (photo: Youd).
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EERI Special Earthquake Report — May 2004

part of the embankment. Neither
crack was wider than a few millimeters. The cracks were caused either
by differential response of the embankment to ground shaking, or byslight settlement within the valley
alluvium or possibly within the embankment. A re-survey of benchmarks on the crest of the dam indicates that as much as 10 mm of settlement occurred between the twocracks during the earthquake. Thecracks were assessed as superficial
and insignificant with respect to theperformance and safety of the dam.

Figure 3. View of reinforced concrete face of the El Khattabi Dam from rightabutment (photo: Youd).

Figure 4. Junction between gravel embankment and concrete gravity sections of theEl Khattabi dam (photo: Youd).

and composed of two primary segments, a 160-m long reinforced
concrete gravity section containing
the outlet works and spillway, anda 460-m-long reinforced concretefaced gravel-fill embankment (Figures 2-5). Following the earthquake,the safety of the dam was of great
concern to the population living
downstream and to the Moroccan
Ministry of Water, the owner and operator of the dam. Because ofthis, the Moroccan government
asked the investigators to make areconnaissance visit to the area toevaluate the condition and stabilityof the dam.

The only earthquake-related effects
noted were two small transverse
cracks in the asphalt-paved roadway
surface on the crest of the dam. The
southerly crack was approximately
above the contact between the eastern edge of a buried concrete slab in
the spillway structure and above thesouthern contact between bedrockon which the spillway structure isfounded and the valley alluvium on
which most of the embankment section is founded. The northern transverse crack was similarly locatedapproximately above the contact
between valley alluvium and bedrock contact beneath the northern
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The exposed reinforced concrete
face of the dam was also examined.
The reservoir was at its maximum
operating level at both the time ofthe earthquake and the time of thevisit, so only the upper 3 m of theface was exposed. There was novisible distress to the concrete slabs
or the joints between the slabs. The
lack of damage to the exposed faceis an indicator that the submerged
face was also undamaged. Had
there been significant damage
to the concrete face or to thejunction between the face and theunderlying slurry-trench cutoff wall,leakage through the dam would
have increased, but the operatorof the dam reported no increase ofleakage.

Joumoua Dam
A 60-m-high roller-compacted-concrete (RCC) dam (Figure 6), located almost 30 km (straight line)
southwest of the epicenter, wasalso inspected. This dam, which
has been operational since 1990,
contained a full reservoir at thetime of the earthquake, with waterflowing over the spillway structure.
A close inspection of this structure
revealed no observable damage,
not even minor cracks.

Building Damage inImzouren
Imzouren is a modern community ofabout 30,000 people located about

EERI Special Earthquake Report — May 2004

7 km northwest of the El Khattabi
Dam and 13 km southeast of theepicenter. Most of the people in thecommunity live in two- to three-story
residential buildings constructedwith ordinary reinforced concrete
frames and clay-tile curtain walls.
The building fronts are generally
finished with painted stucco veneer(Figure 7). The community is underlain by eastward gently sloping
Pliocene conglomeratic sandstoneand alluvium. No evidence of liquefaction or ground deformation wasnoted within this community.

Figure 5 Typical cross section of embankment segment of the El Khattabi dam(Moroccan Ministry of Equipment drawing).

Figure 6. Joumoua Dam, a roller-compacted concrete structure completed in
1990, was undamaged by earthquake shaking (photo: Chraibi).

Figure 7 Collapsed building in foreground and undamaged buildings with typicalconstruction in background (photo: Youd).
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Local regulations require building
permits and architectural drawings
for each constructed building. Inspections are made to assure thatthe building is constructed in accordance with the architectural plans
and that local safety regulations
have been met. No engineering
analysis or inspection of structuralelements is required. Local contractors construct the buildings andare responsible for the sizing andreinforcement of beams and columns. The concrete used in construction is prepared in batch plants
and trucked to construction sites.
The contractors are unlicensed
and unregulated. No educationor special training in construction
practice is available or required.
Newspaper reports indicate that approximately 40 residential buildingscollapsed during the earthquake.
Many additional buildings werecracked and structurally damaged
to varying degrees (Figures 7-8).
Collapsed and seriously damagedbuildings represent only a small
fraction of the total building stock,
but they were the primary causeof the 622 reported casualties.
No serious fires were ignited by
the earthquake. The destruction
caused much distress among the
local population, with many peoplechoosing to sleep in tents or othertemporary shelters rather thanreturn to their homes, damaged orundamaged.

EERI Special Earthquake Report — May 2004

Figure 8. First-story collapse of several
buildings (photo: Youd).

Inspections were being made at thetime of the visit to assess the damage state and safety of each building. Unsafe buildings were marked
with a spray-painted red X (Figure7). Governmental programs werebeing prepared to repair or replacedamaged or collapsed buildings.

Damage Distribution

tabi Dam were undamaged, including a nearby mosque with a tall,
slender minaret. In driving from thedam to the outskirts of Imzouren,
the investigators noted small cracks
in two- and three-story buildings
typical of those in Imzouren. In thecenter of the city, there were numerous collapsed and damaged buildings as well as undamaged buildings. Nearer the epicenter, damage
was slight to nonexistent, with thecity of Al Hoceima (3.5 km northeast of the epicenter) strongly shaken, but reportedly structurally undamaged. Damage may have been
greater at Imzouren because of azone of seismic energy release located closer to Imzouren than to theepicenter, path effects that may
have concentrated seismic energy
in the Imzouren area, or local amplification of damaging groundmotions.

Lifelines
Lifeline services were temporarily
interrupted by the earthquake, bututilities were not badly damaged.
The principal highways into Imzouren remained open to traffic withlittle, if any, obstruction, other thanheavy traffic. The electrical powersystem failed or was temporarilysuspended at the time of the earthquake, but was restored at least to
undamaged areas within 24 hours.
The water system apparently remained in service, because investigators could hear and see waterleaking from damaged buildings fivedays after the temblor.

Response and Recovery
Socioeconomic effects of the earthquake were severe. The injuries
generated demand that exceeded
local emergency services and hospital capability. Aid was rushed tothe area by Morrocan government
agencies and military units. This aid
brought greatly needed assistanceto the damaged communities. Foreign supplies and personnel alsocame to the area within a few days,
providing tents for shelter (Figure9), clothes, food, medicine, andother essentials. Foreign financial
aid, including a gift of $50 million
from Saudi Arabia, has also beenpromised to aid reconstruction of
the area. The promised assistanceof the Moroccan government inrebuilding or repairing structures will
be needed in Imzouren.

Several villages in the hills northwest of Imzouren were severely
damaged. Although reports of casualties and collapse of adobe housing
in these areas had been confirmed,
no media reporters or official investigators had visited these isolatedareas at the time of the reconnaissance visit, nor were the authorsable to do so. The unpaved roads
into the villages were impassible
due most likely to recent heavy
rains, but landslides may also haveblocked some roads. Buildings in
the rural villages were most likely
constructed in typical indigenous
style with rectangular plan, unreinforced adobe walls, and flat earthen
roofs.
With respect to the distribution ofdamage, buildings near the El Khat-Figure 9. Tent city erected in Imzouren to provide temporary housing for people
displaced from their permanent housing units (photo: Youd).
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