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 Algerian Earthquake:Geological setting, source

mechanism, and some lessons

for earthquake hazard in other African coastal cities(Cape Town included)

C.J.H. Hartnady

Cape Disaster Debrief 2004

DMISA Western Cape Branch, 2004 Feb 04

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Algerian Earthquake :2003 May 21 18h 44m 20.1s

Statistics

Epicentre: 36.964ºN 3.634ºEMagnitudes: Mw 6.7; MS 6.9; mb 6.5 (USGS)

Death toll: 2266+

Injured: 10261

Homeless: 150000>1234 buildings damaged or destroyed

Cost: US$100 million(2 m tsunami damaged boats on Balearic Islands)

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Geotectonic Background

Global Plate Tectonics

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NB-EU-NA Plate Motions 

NB

EU

NA

nk lg

goug

suth

hrao

mas1

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African Plate Neotectonics

NB = Nubia

SM = SomaliaUN = Ukerewe

Nyanza

RV = Rovuma

TG = Transgariep

LW - Lwandle<0.5 mm/yr

TG->SM @ ~3 mm/yr

NB->AR

@ ~7 mm/yr

NB->EU

@ ~6 mm/yr

Stable NB

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Hartebeesthoek (HRAO) Motion

GPS velocity of

HRAO

relative to

ITRF2000

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NB-EU Plate Kinematics

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Seismotectonic Framework

L

Am

Ba

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GSHAP: Ibero-Maghreb region

Global

Seismic

HazardAssessment

Program1755

Agadir1960

1365

Historic

earthquake

disasters

El Asnam

1980

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Lisbon – 1 November 1755

Estimated

Magnitude

~ Mw 9

St AlexiusDeath toll > 50000

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Mechanism & Tectonic Setting

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Landsat-7 image of affected area

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Model of slip in fault plane

from Y. Yagi yagi@kenken.go.jp

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Impact on buildings

 Agadir, Morocco 1960

 Africa’s worst earthquake disaster: 

Before and after views ofa tourist hotel

Shallow moderate-strong(M5.9) event on 1960 Feb 29

caused 10000-15000 deaths

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Boumerdes – 21 May 2003

Pieter Strobos  –  Global Relief

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Boumerdes – 21 May 2003

Pieter Strobos  –  Global Relief

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Major Earthquake:

consequences for coastal city Large loss of life and property, due to building

collapse, consequent fires, landslides on

unstable slopes Large-scale disruption of “lifeline” infrastructure;

e.g., sudden breach or failure of dam walls,water mains, disruption of road, rail, or fuel

pipeline links Tsunami inundation of harbours, resorts due to

massive failure on steep continental slope

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Lesotho-KZN Seismic Hazard

Potentialearthquake

risk to:

BloemfonteinMaseruKatse-Mohale

DurbanPietermaritzburgPort ShepstoneRichards Bay

Durban

1860

Pt Shepstone

1942

Zastron

1957

Fauresmith

1912

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SE African Earthquakes

31st December 1932 -offshore St Lucia event

is RSA’s largest (M6.5)earthquake

Beware recurrence of

similar or larger eventscloser to Beira, Maputo,Richards Bay, Durban

1932

1915

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Prehistoric Great Quake:

Bilila-Mtakataka Faulting (M8+)Site A ( S of Lake Malawi):“If the scarp were produced in

a single event, with an averageslip of ~10 m over 100 kmlength, it would be the biggestnormal faulting earthquake

known on the continents” (Jackson & Blenkinsop, 1997, p. 148)

Rukwa 1910

B, C, D = sites of other ~100 km-long,geologically young, surface-breakingfault scarps (major-great palaeoseisms)

MoDs

Be

Mp

PeCt

Db

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Finis