Wet or dry: what causes most destructive earthquakes?

13,000 people die every year in earthquakes.

And while no one can yet accurately predict where and when quakes will actually occur, UTS researchers are improving the ability to understand and mitigate the devastation caused by seismic activity and respond with aid and assistance.

The current paradigm is that the worst conditions for earthquakes are wet ones – that earthquakes occurring after prolonged periods of wet weather cause more devastation to people and the environment as the foundation would be weaker in the wet season.

But new research from UTS contradicts this, showing that an earthquake occurring in/after a prolonged dry weather period is more likely to cause greater damage to infrastructure and to increase loss of life. With greater extremes of weather being reported world-wide, this new knowledge can help many sectors – planning authorities, aid organisations, insurance, engineering and construction – understand the far-reaching impact of a prolonged dry season and to prepare and respond for a major seismic event and its aftershocks.

A study by Associate Professor Behzad Fatahi and Navid Yeganeh (PhD Candidate) at the Centre for Built Infrastructure Research (CBIR) at UTS proves that knowledge of the impact of dry/wet conditions is crucial to planning and building assessment and construction in earthquake-prone zones.

“Damp soil is softer and so absorbs more energy than dry, stiff soil.  After a dry season, during a seismic event a building will experience more load, will move more, will crack more and ultimately be unsafe whether it remains standing or collapses,” said Associate Professor Fatahi.

He and his team apply computer modeling to data from some of the most significant earthquakes experienced (ie the 1994 Northridge earthquake in California caused more than $15billion damage to buildings) to show that after prolonged dry periods such as drought the  devastation is much greater than previously thought.

They can test different building models in a state-of-the art 3-dimensional computer model, examining different soil types, earthquakes and climate conditions.  They are examining seasonal dry season changes in the soil characteristics of moisture content, and the ability of buildings to transfer/absorb energy.

 “While Australia is a relatively stable geological area, our near neighbours in New Zealand, Indonesia and Papua New Guinea for instance, or further afield in the Asia Pacific and beyond experience seismic activity with the potential to cause massive destruction to infrastructure, and major fatalities.  This can impact on Australian businesses working in, or servicing these areas,” he said.

“It is important that urban planners and their construction engineers and partners understand the seasonal effects of wet/dry conditions on soil/ground conditions to better position and build in known earthquake zones.”