Within the last thousand years, humans have modified about three-quarters of the Earth’s surface. This occurs at the local scale via urbanisation, construction of infrastructure, and changing land uses, but also at the global scale, with anthropogenic carbon emissions resulting in climate change. But while these activities might help human development, they have consequences on the geological hazards we live with.

New research led by Professor Emma Hill, Chair of the Asian School of the Environment and Principal Investigator at the Earth Observatory of Singapore (EOS) at Nanyang Technological University Singapore, has shown that various human activities and modifications of our landscape can make landslides, tsunamis, liquefaction after an earthquake worse. The study was published in Nature Reviews Earth & Environment, in collaboration with researchers from ETH Zürich and National Taiwan University.

In the following short video, Professor Emma Hill explains the key tenets of this study and the significance of its findings. Dr Sharadha Sathiakumar, Research Fellow at EOS and co-author on the publication, follows up with details on the 2018 Palu (Indonesia) earthquake, a case study explored in the paper.

As Prof Hill explained, “Earthquake hazards include ground shaking, but secondary hazards are also tsunamis, landslides, liquefaction, which in some cases can be more dangerous than the shaking itself.”

One of the aspects highlighted is how interconnected the Earth systems are. “Everything is connected. As humans if we mess with one part of it, [this] has consequences that we might not initially think about,” said Prof Hill.   

The graphic below, extracted from the paper, displays the complex interconnections between human modifications of the natural environment and the effects on earthquake secondary hazards. A singular human activity can amplify several hazards. For example, groundwater extraction can result in the weakening of the soil in the surrounding area, raising the liquefaction hazard. Groundwater extraction may also cause subsidence of a land area, resulting in a local drop in land height and a rise in relative sea-level. In turn, a higher relative sea-level could increase the vulnerability of a coastal area to tsunami destruction.

Caption: A graphic that shows the interactions between varying types of human modifications to the environment (presented in boxes) and their resulting impacts on earthquake secondary hazards (depicted by hazard symbols) (Source: Figure 4 from the paper published in Nature Reviews) 

In addition, one single earthquake secondary hazard can be amplified by several kinds of human activities. The graphic below illustrates how different human modifications to the environment can increase landslide hazard. Such modifications include local activities, such as the construction of roads and removal of vegetation on slopes, and climate change-related aspects such as increased temperatures and changes in precipitation. These anthropogenic influences can decrease slope stability, and amplify the earthquake-induced landslide hazard. 

Caption: Different human-caused environmental modifications and their influences on landslide hazards. (Source: Figure 1 from the paper published in Nature Reviews)