Earthquake Monitoring: Interpreting the Roar of the Earth

Few natural spectacles are as mesmerizing as a volcano spewing magma accompanied by continuous seismic activity. And we can imagine that few are as dramatic as witnessing a lava flow engulfing your home or business. Both aspects have converged in recent weeks at the Cumbre Vieja volcano on the island of La Palma. On one hand, there are hundreds of visitors drawn to the site by the volcanic activity. On the other hand, there is uncertainty among residents in the area and the significant financial losses caused by the eruption.

However, there is one aspect to be thankful for: zero casualties reported so far. There is no doubt that continuous monitoring and the extensive use of technology have played a role. And in these tasks, Arantec has also contributed its expertise.

How has Arantec helped improve the volcanic early warning systems in the Canary Islands?

Our involvement began with the publication of a public tender by the Volcanological Institute of the Canary Islands (INVOLCAN) in May 2021. The objective was to strengthen the volcano-seismic alert system through the implementation of mobile instrumentation and the development and implementation of innovative methodologies.

La Palma, like other areas with seismic activity, has fixed stations similar to the one shown in the image. These equipment record earthquakes with a magnitude greater than 1.5 on the Richter scale and indicators such as depth and epicenter (if you are curious about the location of these instruments, you can consult the map of seismic stations on the IGN website). The main goal of this surveillance program is to detect changes in the size, speed, and location of seismic events, which can indicate an imminent eruption (1).

Seismic alert network station of Cumbre Vieja – El Paso (La Palma). Source: National Geographic Institute, IGN.

What is the use of mobile stations then? Essentially, their quick deployment and the ability to complement the readings of reference stations, also allowing:

  • Advance early warning in case of a possible eruption.
  • Continue operating effectively during an eruption.
  • Monitor the impact on urban areas and infrastructure in crisis situations.

For example, mobile stations equipped with rotational seismic sensors, which were part of the contract awarded to Arantec, allow for the quantification of seismic energy released during pre-eruption and eruption phases, as well as the real-time characterization of seismic sources.

What does a rotational seismic sensor consist of?

A seismic or earthquake event occurs when energy from processes such as friction between tectonic plates is released in the form of seismic waves. While much of seismic activity has a tectonic origin, the Earth can also vibrate due to:

  • Impact of meteorites
  • Subsidence or collapse of areas
  • Anthropogenic activities such as hydraulic fracturing or fracking
  • Volcanic eruptions, as is the case with the volcano in La Palma. In fact, an earthquake can trigger an eruption, and an eruption can be accompanied by intense seismic activity.

Seismic waves travel in different directions from the focus or hypocenter. One of the instruments used to detect these waves is a seismograph or seismometer, which records vertical and horizontal motion through geophones. These systems can be complemented with seismic accelerometers to measure particle acceleration. However, to obtain a complete picture of seismic activity, it is also important to consider rotational motion along each axis.

Rotational seismology is a relatively recent field of study. One of the earliest experiments to measure this magnitude dates back to 1994. However, the development of rotational sensors, such as the ones provided by Arantec to INVOLCAN, enables a comprehensive analysis of both translational and rotational ground motions.

These types of sensors allow for:

  • Discriminating between different types of waves (shear, pressure, etc.)
  • Measuring wave velocity
  • Increasing the effective sampling of monitoring networks
  • Quantifying the earthquake risk due to rotational motion.

Why is it necessary to monitor seismic activity in a volcanic area?

As pointed out by Saccorotti & Lokmer (1), almost all volcanic eruptions in monitored areas with seismological networks have been preceded by seismic anomalies.

This was the case in the volcano of La Palma, where in the days prior to the lava eruption, more than 6,000 earthquakes were recorded, gradually ascending from a depth of 20 km to the surface (you can see a 3D representation here). And in recent days, for example, it is also happening at Nevado del Ruiz in Colombia, a volcano with infamous history.

Volcanic eruption on the island of La Palma (Canary Islands). Source: National Geographic Institute

The objective of volcanic seismology is to understand the dynamics of a volcanic system. This aspect is particularly relevant considering that magmatic and hydrothermal processes generate a distinct seismic activity that requires specific considerations and procedures.


Few volcanoes are being scrutinized as closely as the Cumbre Vieja volcano. And it is undeniable that the information provided by this intense monitoring will be crucial for improving our understanding of these fiery colossi that dot the planet.

But at Arantec, we trust that all the data being collected will also be used to design more effective warning mechanisms that can keep the population safe. Because that is the purpose of early warning systems: to save lives.

Sources consulted

(1) Saccorotti, G., & Lokmer, I. (2021). A review of seismic methods for monitoring and understanding active volcanoes. Forecasting And Planning For Volcanic Hazards, Risks, And Disasters, 25-73.

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