Induced seismicity

What is induced seismicity?

The term “induced seismicity” is defined as a set of seismic events caused by human activities.
These activities include oil and gas extraction, CO2 storage, clay gas extraction, fracking, geothermal energy production, mining activities, open pit excavations, artificial lakes and dams, and explosions.

How is induced seismicity detected?

Induced seismicity is detected by the same techniques with which natural seismicity of low magnitude is detected. Therefore, dedicated seismic monitoring networks are required to detect very weak events, providing accurate location and magnitude estimates. In some cases, these networks are complemented by instruments installed in deep wells to provide measurements closer to the point where the activities occur. However, no instrumental measurement allows distinguishing between natural and induced events in a certain way.

What causes induced seismicity?

Induced seismicity is due to variations in the state of stress within a rock mass, which are generated by human activities and not by natural causes. If the resulting stress state exceeds the resistance threshold of the material or reduces the cohesion force (i.e., friction) that keeps the faults locked, ruptures or seismic events are produced. The injection of fluids into the sub-surface or their extraction and increases or decreases in the hydrostatic load are the most frequent and documented causes of induced seismicity.

What procedures are adopted in case of induced seismicity?

If the seismic network detects an increase in microseismicity, a more in-depth scientific analysis is carried out to establish a possible link with ongoing activities and the possible evolution of the detected phenomena. In addition to the magnitude and peak values of velocity and acceleration, the analysis considers other parameters, such as the number of events detected, correlation values, and perturbation values of the stress field calculated via numerical modelling.

Is there evidence of seismic events related to gas storage activities?

The HiQuake database ( lists cases of earthquake-induced seismicity around the world. For gas production and/or storage activities, the database lists the following 7 cases in 5 different countries:

  • Gazli, Uzbekistan (Plotnikova et al., 1996) - Storage uses a natural gas production depot that was converted to storage in 1988. Plotnikova et al. (1996) reported seismicity with magnitudes between 4 and 5 during the storage period, especially during the first three years of reservoir filling. Since 1988, storage has been used for gas. It should be noted that the Gazli site is known for two strong earthquakes, M 6.8 in 1976 and M 7.2 in 1984, that occurred during the period of exploitation of the reservoir for gas production, which caused extensive damage and many deaths in the city of Gazli. Therefore, the seismicity detected during the subsequent period of storage may have been related to the two major events that occurred previously. However, the scientific information is rather uncertain because the available literature is mainly in the Russian language.

  • Castor gas storage project, offshore Spain (Cesca et al., 2014; Gaite et al., 2016). - This project aimed to use a depleted oil field (Amposta oil field) consisting of fractured carbonate rocks located offshore in the Gulf of Valencia (northern Spain), approximately 20 km from the coast. A storage capacity of approximately 1.3 billion standard cubic metres of natural gas was planned, sufficient to meet 25% of Spain's storage needs. The seismic sequence began three days after the start of the injections, with increasing events up to ML 2.6. The injection was paused after 12 days, but this was not enough to stop the earthquakes; on the contrary, the strongest Mw 4.3 event occurred two weeks after the injection was interrupted. In total, more than 1000 earthquakes were detected, of which more than 420 had ML ≥ 2. Weak seismicity was still ongoing in 2016 (Gaite et al., 2016). The seismic sequence induced by the storage at Castor led to a strong negative public reaction because the population was very sensitive to the problem of seismic risk after the Mw 5.1 earthquake in Lorca (approximately 250 km farther south along the coast) in 2011. Following the earthquakes that occurred, the project was suspended. In retrospect, it was recognized that the gas injection activities reactivated a fault in the Amposta fault system. In addition, both the seismic monitoring infrastructure and especially the ability to analyse the seismic data collected in an effective and timely fashion were found to be inadequate.

  • Bergermeer, Norg and Grijpskerk storage camps in the Netherlands (Anonymous, 2014). For these cases, only very limited numbers of very weak events are reported, for which no scientific study has yet been published. The only documented evidence concerns some microevents with a maximum magnitude of 0.7 that occurred in 2013 at the Bergemeer repository during the cushion gas creation phase and were detected by microseismic arrays dropped into the well. Additionally, in this case, it is important to distinguish these activities from the better known gas production activity in Groeningen that has caused some known earthquakes reported in the literature.

  • Háje, Czech Republic (Benetatos et al., 2013; Zedník et al., 2001) - Storage used underground caverns, and two earthquakes of magnitude 0.2 and 0.4 were recorded near the area in 2009. 

  • Hutubi, China (Tang et al., 2015; Zhou et al., 2019) - Storage used a natural gas production depot that was converted to storage in 2013. Approximately 200 events were detected during the first gas injection cycles, with two major events of M 2.7 and M 3.0 in 2013 and some minor events in 2014, approximately 3 km and 1 km from the reservoir, respectively. The most recent study (Zhou et al., 2019) consider that these events were induced and caused by the reactivation of pre-existing faults due to the spread of poro-elastic stress.

Finally, Evans et al. (2015) reported a case of microseismicity (even better classified as nano-seismicity) detected at the storage of Germigny (northern France, aquifer storage), which has been operational since 1982. In the period between 1991 and 1992, microseismicity was detected at the instrumental level (less than 30 events), detected only by sensors dropped into deep wells and located in the production layer near the injection wells (Deflandre et al., 1993; Fabriol, 1993).

In Italy, is there evidence of seismic events related to gas storage activities?

In Italy, there is no evidence of events related to gas storage activities.

It should be considered on the one hand that gas storage in Italy is carried out exclusively in depleted gas depots, and this type of storage is considered particularly safe. In many cases, the seismic monitoring of gas storage is carried out by the same (private) entity that performs the storage. However, for the storage of Collalto (TV), which is monitored with a dedicated seismic network by a public research organization (OGS) and whose data and analysis are public, there is also an absence of seismicity related to the storage activity.