What Are The Long Term Trends?

Supporters of the theory that anthropogenic climate change could trigger a greater number of earthquakes are likely to refer the long term record of earthquake events. I came across the graph below from a USGS ‘Earthquake Project’ which aims to analyse earthquake trends. The figure clearly shows that in recent years the number of all earthquakes has shot up.

However, a graph like this can be misleading. For one thing the scale merely spans a 30 year time frame dating back to the mid-1970s therefore is unsuitable for assessing long term trends. More importantly, this ascending pattern can be suitably associated with the launch of a global network of seismograph stations capable of discerning low intensity earthquakes. Such ground movement was undetectable up until 25 years ago. A solution is to include only the earthquakes reported to be magnitude 7 or above – all these events would have been detectable with fewer stations using less advanced technology.  Nonetheless, it is difficult to ascertain how accurate the earthquake record is during the 19^th century. There is likely to be some incomplete data, therefore data sets may underestimate the occurrence of earthquakes before 1901. I have found that it is important to consider that this field of science is riddled with uncertainties and that a long term hazard record must be scrutinised. 

The data below comes from the USGS. The relatively long time ranges (38 years) summarise how earthquake activity since 1901 has been continuously increasing. Having excluded all low intensity events, the figures suggest that more major earthquakes are occurring now.

1901 to 1938 - 53 earthquakes

1939 to 1976 - 71 earthquakes

1977 to 2014 (2011) – 164 earthquakes

Is this upward trend enough to make us believe that nature has finally risen up to combat human domination? Too many scientists surmise that the data above is tangible evidence to prove that the trend will continue to climb. The effects that anthropogenic climate change has on the inner workings of the Earth are far from certain and past events must be interpreted with consideration. Unquestionably the statistics allude to the fact that we are in a period of increased tectonic activity, but without establishing the cause it is unclear whether this trend will be sustained.