24.05.2016: When mountains form by tectonic processes, this is often accompanied by violent events: earthquakes changing the landscape. This can happen in two ways: earthquakes build topography either by surface uplift or they destroy it through the landsliding they set off. Using a new model, researchers of the GFZ, together with a colleague from the Ecole Normale Superieure in Paris, have found out that intermediate size earthquakes (magnitudes between 6.3 and 7.3) can cause more erosion than uplift. Larger earthquakes with a magnitude of more than 8 are predicted to nearly always be constructive.

Better understanding of mountain formation

“The term ‘constructive’ by no means implies that the larger earthquakes are less harmful”, says author Niels Hovius. “We classified the events by mass balance of the regions affected.” The study by Odin Marc, Niels Hovius (both GFZ) and Patrick Meunier (ENS Paris) is published in Geophysical Research Letters. The findings help understand mass transport during mountain formation and may lead to more precise models of surface processes and orogenesis.   

“Our study suggests that the role of earthquakes in topography and mountain building is changing as the geological faults are growing and maturing”, says first author Odin Marc. In contrast to previous studies that have not considered the specifics of faulting and topography, the researchers have found that earthquakes with a net erosive effect are those within a window of intermediate magnitudes. The findings apply to shallow earthquakes. These events are seen as the major driver of rock uplift in mountainous regions. For deeper earthquakes or for landscapes with gentle topography this window of magnitudes may narrow or disappear.

The authors stress that their study does not challenge the role of earthquakes as a key mechanism of mountain building. Rather, it demonstrates that earthquakes are ambivalent agents, which may limit topographic growth during a given period or in a certain part of a mountain belt. In the Himalaya region, for instance, very large earthquakes likely drive topographic growth. In regions with smaller mountain belts, such as Taiwan, the average topographic uplift and landscape formation may be limited rather than supported by earthquakes.

Marc, O., Hovius, N., Meunier, P., 2016. The Mass Balance of Earthquakes and Earthquake Sequences. Geophysical Research Letters. DOI: 10.1002/2016GL068333

>>Feature on the topic in the scientific journal Nature