Lessons from some of the more recent earthquakes (2000-2019)
Lessons from some of the more recent earthquakes (2000-2019)
Uploaded At: 01 May 2024Lessons from some of the more recent earthquakes (2000-2019)
The 2004 Niigata-ken Chuetsu earthquake (MW=6.6) hit the central area of Japan causing many coseismic landslides in soft sedimentary rocks (Figure 1) and significant damage to the regional road network (Figure 2). Slope failures also occurred in residential areas due to low seismic resistance of embankments. It is noteworthy that several tunnels were severely damaged in this event due to significant ground deformation (Figure 3). A range of issues attracted engineering attention following this earthquake including the need for a better protection of private properties from earthquake damage, the necessity for efficient drainage systems in natural dams formed by landslides, and damage to tunnels in soft rocks. In the 2007 Niigata Chuetsu-oki earthquake (MW=6.8), the causative source as close as 15 km to the site of Kashiwasaki Nuclear Power Plant. The power plant was shaken intensely with a peak acceleration of nearly 0.7 g, however, there was practically no damage to the main reactor building despite the fact that the accelerations significantly exceeded the design level.
Figure. 1 Coseismic failure of soft-rock mountain and collapse of highway
Figure 2. Seismic failure of road embankment
Figure 3. Heaving of invert in road tunnel associated with compression-bending failure at the internal surface of concrete at the crown
The 2005 Kashmir-North Pakistan earthquake (MW=7.6) caused over 80,000 fatalities. The town of Balakot was hit especially hard, with approximately 90% of the buildings destroyed due to severe ground shaking and landslides. Topographical amplification of the earthquake motions (Figure 4) and fault-rupture induced slope instability are two noteworthy observations from a geotechnical viewpoint. This earthquake also demonstrated that long-term slope instability in areas hit by strong earthquakes due to cascading effects associated with strong precipitation.
Figure 4. Building damage in Balakot due to topographic amplification of earthquake motion. foot hill area (left), top of the hill where the buildings are totally destroyed (right)
The 2008 Wenchuan earthquake (MW=8.0) was the biggest earthquake in China since the 1950s. It affected a region of 500.000 km2, almost 90,000 people were killed, and the economic losses were about 900 billion Chinese Yuan (about US$150 billion). The fault-rupture itself (approximately 200 km long with a dislocation of 5.5m horizontal and 6.4m vertical) destroyed numerous buildings and infrastructures. The earthquake caused about 21,000 landslides and debris flows, which buried buildings, houses, highways, railways, farmland, and dammed rivers creating 34 barrier lakes. Urgent works had to be carried out after the huge Tangjiashan landslide blocked Bailongjiang river to form a large barrier lake with a volume of 20 million m3. The water depth of 60-80m in the lake continuously rising created high risk of flooding affecting about 1.2 million people in two cities and many villages downstream. The rainfalls after the Wenchuan earthquake, triggered many landslides on seismically affected slopes and debris flows along the valley with accumulated sliding soil mass for a long time, which is attributed to the compound effects of earthquake and rainfall. The Wenchuan 8.0 earthquake triggered many actions in China regarding the including revision of the seismic hazard map, the design seismic code for buildings and infrastructure, and the development of systems for risk assessment, monitoring, early-warning and prevention of landslides and debris flow.
Unlike the relatively quiet period for earthquakes with magnitudes >8.5 at the end of the 20th century (from 1970 till 2000), several gigantic earthquakes of magnitude greater than 8.5 (and even greater than 9.0) occurred after 2000. These massive earthquakes highlighted the need to reconsider seismic demand at the high end of the scale, given that empirical knowledge from previous events did not include observations from such large-magnitude events. The 2004 Indian Ocean (Sumatra-Andman) earthquake (MW=9.1) and the 2011 Tohoku earthquake (MW=9.0) caused huge tsunami disasters with a large number of fatalities (over 220,000 and over 20,000, respectively). These tsunami disasters showed that seawalls are essential infrastructure to protect near-shore communities from tsunami, and also demonstrated that levees along the coastline and river channels are generally poorly protected against water overtopping and scouring. It is recognized, however, that these vulnerabilities are associated with significant uncertainties in the evaluation of the tsunami hazard.
The 2011 Tohoku earthquake (MW=9.0) exerted profound effects on the entire country of Japan both economically and physically. From a geotechnical viewpoint, the damage caused by the tsunami, the incidents at nuclear power plants, and liquefaction and instability of manmade fills are noteworthy. Seawalls along the coast did not effectively mitigate the tsunami disaster, partially because they were not high enough and partially because some of them were scoured and washed away by the overtopping tsunami water. Another interesting observation is that to prevent buildings from overturning it is necessary to design pile foundations with the tsunami exerted strong lateral forces (Figure 5). The main lesson learnt from the nuclear incident at the Fukushima Dai-ichi (No.1) Power Plant is that it would be very important to provide tsunami safety measure for nuclear power plants. Serious geotechnical engineering implication in the recovery process, e.g. cleaning of contaminated surface soils, construction of submarine water tunnels for discharge of treated waters into sea, and underground repository of the contaminated materials, are some of the major challenges. Another interesting lesson is that liquefaction mitigation measures for individual residential buildings is very difficult to be undertaken by the population alone without a strong involvement of the government and the insurance industry.
Figure 5. Tsunami impacts: overturned building previously on piled foundations.
The 2009 L’Aquila earthquake (MW=6.3) seriously damaged historical and monumental buildings and churches in L’Aquila, Italy. The importance of the damage and numerous available strong motion recordings in the affected area triggered a vast number of studies to understand the role of site and basin effects, to improve their modeling and examine the role that soil-structure interaction SSI might have played in the response and vulnerability of monumental structures. An important consequence of this event is the decision to conduct detailed microzonation studies in most Italian cities.
The 2010 Haiti earthquake (MW=7.0) caused over 230,000 deaths and showed clear correlation between the geological/soil conditions and building damage. A high rate of damage rate was observed in the Holocene alluvium sites due to site amplification of ground motion and concentration of poorly reinforced, 2 to 5-story RC buildings. Severe damage occurred in the harbor of Port-au-Prince due to soil liquefaction, and strong evidence indicated the existences of submarine landslides similar to what occurred along the shore of Izmit Bay in Turkey during the 1999 Kocaeli earthquake.
In 2010, a mega thrust-faulting type earthquake (MW = 8.8) struck the Central-South region of Chile. The earthquake and the tsunami caused near 600 casualties and a direct cost of about US$30 billion. The rupture zone of this earthquake covered a rectangular area of approximately 550 km by 170 km on the interface between the two tectonic plates, Nazca and South American. Permanent displacements on rock outcrops measured after the earthquake in Arauco Peninsula reached an uplift of 1.8 m and a horizontal displacement of 5.1 m towards the sea. Significant damages were reported in road infrastructure, railroads system, ports, buildings and houses, agriculture terrains, irrigation channels, tailings dams, among others. The failures of pile foundations induced by lateral spreading produced a serious impact on the operation of ports and industrial buildings. The seismic behaviour of the buildings was excellent, except for two cases with collapse, proving that the characteristic Chilean building with the use of shear walls is a good seismic structural solution. It was shown that tailings dams built using the upstream construction method are seismically unsafe.
In 2010 and 2011, a series of strong earthquakes from local sources (MW=6.2 to 7.1) hit Canterbury and the City of Christchurch, New Zealand. The February 2011 Christchurch earthquake (MW=6.2) was particularly devastating causing 185 fatalities, damage to multi-storey buildings in the central area of the city and widespread liquefaction over nearly half of the residential area, generating arguably the worst urban liquefaction on record (Figure 6). 20,000 residential buildings suffered severe damage in the foundations and underlying soils, and many modern buildings on shallow foundations in the city centre exhibited significant deformation/subsidence/tilt and loss of serviceability due to soil liquefaction. A key legacy of the earthquakes has been the formation of the New Zealand Geotechnical Database – a platform which provided free access to site investigation across the city (and later the whole of New Zealand) and has formed a critical part of many research studies. An abundance of well-documented case histories, comprehensive laboratory and field investigations, and detailed research studies provided basis for substantial improvement of methodologies and databases for evaluation of soil liquefaction and lateral spreading, and their implementation in New Zealand and international practice.
Figure 6. Liquefaction in residential area of Christchurch, NZ
The 2016 Kaikoura, New Zealand earthquake (MW=7.8) caused numerous landslides and 150 km-long surface fault rupture in the source area. The earthquake caused substantial damage to several modern multi-storey buildings in Wellington due to prominent site amplification and basin edge effects. Widespread liquefaction occurred in thick gravelly reclamations at the Wellington port affecting piled wharves and buildings on shallow and deep foundations, and serves as a reminder that pre-existing critical infrastructure may require re-assessment for seismic vulnerability. Well-documented case histories and comprehensive research studies were used to upgrade engineering practice in dealing with these complex geotechnical problems.
The 2015 Gorkha, Nepal earthquake (MW=7.8) caused nearly 9,000 fatalities. From a geotechnical viewpoint, the most important lessons learnt were the basin effects observed in the Kathmandu Basin, and the observed co-seismic landslides that were likely caused by the combination of directivity effects and the infiltration of snow/ice-melt water into potentially unstable slopes which increased the risk of both gravitational and co-seismic landslides.
Other earthquakes with marked geotechnical impacts include the 2018 Sulawesi, Indonesia earthquake, 2018, in which flowslides occurred (at Balaroa, Petobo, Jono Oge, and Sibalaya) in gently sloping ground of less than 5% producing extremely large movements of several hundred meters. While soil liquefaction was clearly contributing to the observed phenomena, the mechanism behind such large displacements are yet to be fully explained. The 2017 Puebla, Mexico earthquake (MW=7.1), produced similar ground motions on top of the soft clay in Mexicon city as the Michoacan 1985 devastating earthquake, as a result of soil amplification, despite the differences in magnitudes, mechanisms, and source-to-site distances between the two earthquakes, thus providing important verification for the one-dimensional site response theory.
Recent European earthquakes (e.g., 2012 Emilia-Romagna, Italy earthquake, 2014 Kafalonia (MW=6.1), and 2015 Lefkada (MW=6.5) earthquakes in Greece also highlighted the role of local ground conditions and site effects on ground motion characteristics and severity of damage. The ongoing revision of Eurocode 8 is another illustration of the recognized importance of site amplification effects with factors that are not only site-class dependent but also intensity dependent due to soil nonlinearity.
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