Monthly Archives: May 2024

Natural disaster warning system (LUOVA)

Structure and functioning of LUOVA

The LUOVA system gathers forecasts, assessments, and warnings from various sources, and creates a real-time situational picture to support the decisions of the authorities. The basis of LUOVA is an information system that enables research institutes to monitor different natural phenomena worldwide and analyze threats, risks, and actual natural disasters. LUOVA offers a uniform reporting method for all types of warnings – one, fast channel in which authorities find the necessary information about natural disasters.

The LUOVA operation center is located at the Finnish Meteorological Institute (FMI) together with the on-call weather services. Experts deliver real-time reviews on natural disasters to the LUOVA web portal. Information providers of LUOVA are Finnish Meteorological Institute (dangerous weather phenomena, sea floods, tsunamis), SYKE (water floods) and the Institute of Seismology (earthquakes, tsunamis).

Earthquake observations in LUOVA

Institute of Seismology provides information and assessments of hazardous impacts of earthquakes to the LUOVA system. The focus is on hazardously big earthquakes abroad mainly at the tourist but also at high-risk destinations, but authorities are also informed about notable earthquakes in Finland. The earthquake alerts and estimates of the LUOVA are based on the Institute’s automatic observation system and on the on-call duty related to it. The on-call seismologist gets information on earthquakes primarily from the SeisComP-based automated system. More information on the events can be found on the websites of international organizations and centers, and on their warning messages.

The on-call seismologist checks, evaluates, and corrects automatic alerts. The risk of the event is assessed, and the event is classified into risk categories 1-4 (1 = extremely dangerous, 2 = dangerous, 3 = potentially dangerous, 4 = not dangerous). The on-call seismologist provides an impact assessment with a more detailed description of the possible consequences for the risk categories 1 to 3 events via the LUOVA system to the authorities. In addition, on-call seismologists will provide an expert opinion and assistance in issuing warnings and assessing the effects of damage, if necessary.

In 2023, 296 events came to the LUOVA system. Of these, 237 were evaluated as risk category 4 events, 51 risk category 3 events, 6 risk category 2 events and 2 risk category 1 events.

Assessment of effects caused by earthquakes

The magnitude of an earthquake and the earthquake effects and consequences are not directly interdependent. When assessing the destructive effects, without direct observations from the event area, priority is given to the magnitude of the earthquake (released energy, destructive power) as well as to the depth of the earthquake (surface waves, tsunami) and the location of the earthquake (centers of population, age and condition of buildings, critical infrastructure). That is, even a small earthquake (magnitude 4-5) occurring at shallow depth below a large population center can cause great damage. On the other hand, a large earthquake (magnitude 6 – 7) in the middle of the wilderness or ocean may not attract any attention (other than that it is detected by the global seismic station network).

Tsunamis relate to large earthquakes (typically above magnitude 7) that occur on the seabed due to vertical movement. Therefore, tsunamis are most commonly generated in subduction zones. Tsunami is different from wind-generated waves in such a way that it puts in motion the sea water in motion at its entire depth, while the effect of wind-generated waves is limited to the surface layer. Tsunami wavelengths and speeds are also significantly higher. The LUOVA on-call seismologist will also issue a warning in connection with the impact assessment if a tsunami can arise from an earthquake.

Recent earthquakes globally can be found on the Institute’s website (https://www.helsinki.fi/en/institute-seismology/earthquakes/earthquakes-globally).

Niina Junno, seismologist

Daily analysis of seismic events investigates the sources of seismic signals

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The Institute of Seismology frequently receives inquiries from the media and citizens about various shaking observations.

The Institute has several channels to report or send inquiries on these observations. In addition to calling the info-phone of the Institute of Seismology, you can send an email or fill out an observation form on our website. Links and other contact information can be found on the Institute’s website. Every observation will be examined, and if necessary, we will carry out an analysis of the event. An explanation cannot always be found simply by looking seismograms, as some of the event sources are very weak and local. In these cases, only a very close seismic station can detect the signal. On the other hand, the source may be elsewhere than in bedrock, for example, an air-borne pressure wave can also cause windows to vibrate.

Based on the observation sent to us, we check the data from the nearest seismic stations for the time indicated. If the seismic event is strong enough, it may already be visible on our website “Seismic bulletins” where you can find “Local explosions and earthquakes today“. This page contains a map and a list of seismic events automatically detected and located by our software system. Because it is an automated list, i.e. a person has not checked it, the locations can be inaccurate at times, and there may even be incorrect events when the software combines signal peaks caused by frost, for example.

An analyst, i.e. a seismic data analyzer, searches for data from seismic stations at the requested observation time. Data is searched for a possible seismic event, the source of which is usually an explosion or an earthquake, but sometimes cave-in, landslide or frost quake can cause a signal. The first signal is marked as the longitudinal wave or P wave, and a slightly slower wave is marked as transverse wave or S wave. When these waves have been determined for several seismic stations, the difference in the velocity between P and S waves can be used to calculate the distance between the source and the station, and the source of the signal is likely to be found at or near the intersection of these distances. The more seismic stations are available around the source, the more precise location can be determined for the event. For example, seismic events in Finland tend to be located closer to the real source than seismic events outside Finland.

The analyst will also try to determine the seismic event mechanism as best as possible. Most seismic events observed in Finland (about 18,000 per year) are explosions at mines, quarries or construction sites. Explosions in mines and quarries are typically made as a series of multiple blasts, where bets are placed at certain distances from each other and are detonated with a slight delay. For explosions such as these, the signal is characterized by a steady distribution of energy in all directions and the typical waveforms generated by different blasting techniques (Figure 1). The explosions aim to dampen some energy frequencies and typically form a striped pattern in energy spectra (Figure 2).

Figure 1. Typical signal from an explosion observed in seismograms.

Figure 2. Typical striped energy distribution caused by an explosion. The left vertical axis denotes frequency, and the color scale describes the signal strength (i.e. the amount of energy). The image shows the OUF station’s observation of the explosion at Kaustinen.

However, with earthquakes, energy is distributed in different directions depending on the type of movement in the bedrock that caused the signal (Figure 3). In the energy spectra of the earthquake, energy has been distributed evenly across all frequencies, especially at closer seismic stations (Figure 4). A small seismic event, overlying locations, or duplication of another seismic event can make it more difficult to determine the source.

Figure 3. Earthquake happened in Kuusamo on 2 May 2024. Figure shows registrations from different seismic stations in Finland.

Figure 4. The energy distribution produced by the Kuusamo quake (from MSF station) is characteristic of the earthquake. The left vertical axis denotes frequency, and the color scale describes the signal strength (i.e. the amount of energy).

Finally, the analyst determines the magnitude of the event by measuring the amplitude of the strongest signal at different stations, from which the local magnitude is calculated to the seismic event. Once all parameters have been obtained, the result will be published on our website. Earthquakes are immediately visible through an earthquake search. In addition, earthquakes will appear within a few working days after the remaining seismic events of that day have been analysed, “Seismic bulletins” from the tab “Analyst-reviewed bulletins” of the page “daily bulletins of seismic events in Northern Europe” with explosions and other seismic events.

Kati Oinonen, seismologist

Environmental Seismology – Monitoring More than Earthquakes

When Noise is not Noise

As more and more sensitive instruments were installed around the world, seismologists noticed that, instead of being quiet, the earth was constantly humming with energy. This energy was usually quieter than signals generated by earthquakes, but easily detected with high-quality instruments.

Figure 1: Energy recorded at different seismic periods over 5 years of data from station KEV in Finland and station WRAB in Australia. Peak values at periods of 3-5 seconds (red arrows) are related to energy generated by ocean waves. Plots were generated using EarthScope MUSTANG web services [1].

Figure 1 [1] shows the energy recorded at two different seismometers over 5 years. Station KEV is located near the village of Kevo in Lapland, and station WRAB is in central Australia. Even though they are in two very different places geologically, the energy pattern looks quite similar, with a peak of energy around 3-5 seconds period (0.2-0.33 Hz in frequency). This energy pattern is seen every day, on nearly every seismic station on earth, and while scientists long suspected that this noise is coming from waves interacting in the oceans [2], it was only recently that this was able to be accurately verified [3].

Air, Ice, and Rock

Other earth processes also generate signals that either older seismic equipment could not measure, or we lacked the necessary number of stations nearby, or we did not have the necessary computational power to decode the signals until recently. For example, scientists have been able to track thunderstorms moving across the southern United States [4], and calculate the strength of cyclones in the Pacific Ocean [5], using only seismic data.

As glaciers have been rapidly retreating due to climate change, seismology can also be used to detect glacial surges [6] or small caving events, even being able to determine the direction that the ice fell [7].

Seismic data is even being used to monitor for landslides in near real-time, watching for a landslide that could generate a potentially dangerous tsunami (figure 2) [8]. Monitoring for signals like these are similar in theory to how regular earthquakes are detected and located but using completely new methods to interpret the seismic data and doing it rapidly enough to potentially alert people in danger before the threat arrives.

Figure 2: From Karasözen and West (2024), nine automatically detected landslides at fjords in Alaska using seismic data.

We are in an exciting era of seismology, where many of the technological limitations of previous generations have been lifted. We can use seismology to move past only monitoring for earthquakes and use the tools and our creativity to learn more about the earth system as a whole – the atmosphere, the oceans, and the rock beneath our feet.

Matt Gardine, seismologist

References

[1] Casey, Robert, Mary E. Templeton, Gillian Sharer, Laura Keyson, Bruce R. Weertman, and Tim Ahern. “Assuring the Quality of EarthScope Data with MUSTANG”. Seismological Research Letters 89 (2A) (2018): 630-639. https://doi.org/10.1785/0220170191

[2] Longuet-Higgins, Michael. S. “A theory of the origin of microseisms”. Proc. R. Soc. London Ser. A 243 (1950): 1–35.

[3] Kedar, Sharon, Michael Longuet-Higgins, Frank Webb, Nicholas Graham, Robert Clayton, and Cathleen Jones. “The origin of deep ocean microseisms in the North Atlantic Ocean”. Proc. R. Soc. London Ser. A 464 (2008): 1–35. https://doi.org/10.1098/rspa.2007.0277

[4] Tytell, Jonathan, Frank Vernon, Michael Hedlin, Catherine de Groot Hedlin, Juan Reyes, Bob Busby, Katrin Hafner, and Jennifer Eakins. “The USArray Transportable Array as a Platform for Weather Observation and Research”. Bulletin of the American Meteorological Society 97.4 (2016): 603-619. https://doi.org/10.1175/BAMS-D-14-00204.1

[5] Gualtieri, Lucia, Suzana J. Camargo, Salvatore Pascale, Flavio M.E. Pons, and Göran Ekström. “The persistent signature of tropical cyclones in ambient seismic noise”. Earth and Planetary Science Letters 484 (2018): 287-294. https://doi.org/10.1016/j.epsl.2017.12.026

[6] Nettles, Meredith, and Göran Ekström. “Glacial earthquakes in Greenland and Antarctica”. Annual Review of Earth and Planetary Sciences 38:1 (2010): 467-491. https://doi.org/10.1146/annurev-earth-040809-152414

[7] Olsen, Kira G., and Meredith Nettles. “Constraints on terminus dynamics at Greenland glaciers from small glacial earthquakes”. Journal of Geophysical Research: Earth Surface 124 (2019): 1899–1918 https://doi.org/10.1029/2019JF005054

[8] Karasözen, Ezgi, and Michael E. West. “Toward the Rapid Seismic Assessment of Landslides in Coastal Alaska”. The Seismic Record 4 (1) (2024): 43–51 https://doi.org/10.1785/0320230044

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