We have received many questions about the seismic activity in La Palma island displayed on our maps. Indeed many of you reporder this grid effect
[Picture and caption from a user, doubting it can be natural]
Others wondered about tsunami risk or if it meant that these earthquakes were not caused by unatural sources.
Indeed, when looking at the map at this size, it looks very unusual. Actually, this “grid” of earthquake locations is an artefact, due to the fact that the EMSC rounds longitude and latitude coordinates to two decimal points.
We take this occasion to explain why the EMSC map displayed a grid pattern of earthquake locations in La Palma island. If you look at the longitude and latitude data provided by EMSC (Earthquakes - Earthquake today - Latest Earthquakes in the World - EMSC), you will see that there are two decimal points in each value, resulting in a less-granular, less-defined dataset.
As a way of example, Google Earth uses 6 decimal points for the lon/lat couples. This allows for exponentially more granularity, which results in a higher-definition display.
In tight earthquake clusters like the ones occurring in La Palma, when you zoom way in, the 2 decimal point approximation creates an artefact and the earthquake locations are displayed like a grid.
This artefact is not unique to La Palma. It happens everywhere on our maps, whenever there is a huge zoom on a very small area. In La Palma, the artefact is pronounced because of the very small size of the island.
IGN, the authoritative source for seismic information in Spain, does not round the coordinates, and the seismicity does not look like a grid on their map:
Visualizador Terremotos Próximos.
We recommend consulting the local sources for tight seismicity like the one we are observing in La Palma.
Instituto Geográfico Nacional, IGN
Website: Instituto Geográfico Nacional
Instituto Volcanológico de Canarias
We are sorry for this misunderstanding and are glad of this opportunity to exchange with you and better explain our services.
In short … yes this activity is natural, and no there is not going to be a mega tsunami