Civil Engineering Reference
In-Depth Information
several buildings and bridges (Figure 1.27) because of horizontal movements. Quay walls and sea
defences in the port of Kobe were also affected by soil liquefaction.
(iv) Landslides
Landslides include several types of ground failure and movement, such as rockfalls, deep failure of
slopes and shallow debris fl ows. These failures are generated by the loss of shear strength in the soil.
Landslides triggered by earthquakes sometimes cause more destruction than the earthquakes them-
selves. Immediate dangers from landslides are the destruction of buildings on or in the vicinity of the
slopes with possible fatalities as rocks, mud and water slide downhill or downstream. Electrical, water,
gas and sewage lines may be broken by landslides. The size of the area affected by earthquake- induced
landslides depends on the magnitude of the earthquake, its focal depth, the topography and geologic
conditions near the causative fault, and the amplitude, frequency content and duration of ground
shaking. During the 1964 Alaska earthquake, shock-induced landslides devastated the Turnagain
Heights residential development and many downtown areas in Anchorage. One of the most spectacular
landslides observed, involving about 9.6 million cubic metres of soil, took place in the Anchorage area.
The scale of such landslides on natural slopes can be large enough to devastate entire villages or towns,
such as the Huascaran Avalanche triggered by the Peru earthquake (1970,
M
w
= 7.8). Most of the more
than 1,000 landslides and rockfalls occurred in the epicentral zone in the Santa Cruz Mountains during
the 1989 Loma Prieta earthquake. One slide, on State Highway 17, disrupted traffi c for about 1 month.
In the 1994 Northridge earthquake, landslides that occurred in Santa Monica, along the Pacifi c Coast
Highway, caused damage to several family houses built on the cliffs overlooking the ocean. This is
shown in Figure 1.28. Relatively few landslides were triggered by the Hyogo- ken Nanbu earthquake
in Japan. This is partly due to the fact that the earthquake occurred during the dry season. Landslides
are often triggered by rainfall pressure generated inside fractured ground.
In the Kashmir earthquake of 8 October 2005, land-sliding and critical slope stability was a multi-
scale problem that ranged from limited sloughing of a superfi cial nature to a scale that encompassed
entire mountain sides (Durrani
et al
., 2005). The land-sliding problem in the mountains of Azad Jammu
and Kashmir and North West Frontier Province, Pakistan, has similarities to land- sliding that occurred
in the mountains of Central Taiwan due to the 1999 Chi-Chi earthquake. Figure 1.28 shows a large-
scale landslide in the Neela Dandi Mountain to the north of Muzaffarabad. The satellite image shows
that the landslide blocked the Jhelum River.
Problem 1.5
The 17 August 1999 Kocaeli (
M
w
= 7.4) and 12 November 1999 Dü zce (
M
w
= 7.2) earthquakes
were the largest natural disasters of the twentieth century in Turkey after the 1939 Erzincan earth-
quake. These earthquakes caused severe damage and collapse especially of building structures.
Figure 1.29 shows typical damage observed in the city of Izmit (Kocaeli earthquake). The collapse
of a multi-storey reinforced concrete building in Izmit (Düzce earthquake) is also provided in the
fi gure. Correlate the surveyed failure with the earthquake-induced ground effects illustrated in
Section 1.4.2.
1.4.3 Human and Financial Losses
During the twentieth century, over 1,200 destructive earthquakes occurred worldwide and caused
damage estimated at more than $10 billion (Coburn and Spence, 2002). If these costs are averaged over
the century, annual losses are about $10 billion. Monetary losses from earthquakes are increasing
rapidly. Between 1990 and 1999, annual loss rates were estimated at $20 billion, twice the average
