Current Global Seismic Activity Level (GSAL)
Updated: Nov 19, 2023 17:38 GMT -
In order to find out whether worldwide earthquake activity has been increasing or decreasing or at which level it is now compared to the past, check out our Global Seismic Activity Level
charts below. Feel free to embed the graphics on your own website if you like!
For detailed stats on the level of activity now compared to earlier, check the Quake-O-Meter
How this value is calculated and what it means
The Global Seismic Activity Level (GSAL) was developed by geologist and volcanologist Tom Pfeiffer PhD for VolcanoDiscovery, as an online tool to visualize current levels of seismic activity on a global scale. It is based on the averages of all earthquakes during a given time interval.
GSAL is a numeric value ranging from 0-10 indicating the current level, from low to extreme, of seismic activity worldwide. It is calculated by combining the energy of all known earthquakes worldwide during a given time interval (default being the past 24 hours). It corresponds to the theoretical magnitude of all earthquakes during the specified time interval occurring together in single event. This value represents a moving average which changes constantly as new earthquakes occur. It allows to monitor the appearance of clusters of larger quakes around the world, and typically fluctuates around moderate ("green") levels around values of 6.0.
For instance: if the level for one day is at 6.3, it means that if all earthquakes in the world occurred together as one, it would be at around magnitude 6.3.
GSAL furthermore takes into account:
- It is assumed that all quakes above magnitude 5 are being recorded; these quakes are weighted by a factor of 1.
- It is also assumed that a significant number of smaller magnitude quakes go unnoticed as global coverage by seismic networks is not able to detect all quakes below magnitude 5. Based on statistical information from areas with very good coverage of even small quakes (such as in California, Italy etc), a small correction for the true number of small quakes beneath magnitude 5 is applied. This weight factor for smaller quakes ranges from 1.3 for quakes within magnitudes 4.5-4.9 to 5 times for quakes between magnitude 2.0-2.9.
However, as the larger quakes contribute so much much more to the global energy release than all smaller combined, the effect of this correction, i.e. assuming more of the smaller quakes than recorded, is actually quite small.