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2020-06-23, M7.4, Oaxaca, Mexico

At 15:29:05 (Universal Time) on the 23rd of June 2020, an earthquake of magnitude 7.4 struck in the Oaxaca region of Mexico (see map below). The earthquake occurred at a depth of 10 km, locating approximately 12 km SSW of Santa Maria Zapotitlan, Mexico. Shortly after, the Pacific Tsunami Warning Canter (PTWC) issued a warning that hazardous tsunami waves  reaching 1 to 3 m above the tide level along the coast of Mexico are possible.

Mexico is one the earths most seismically active regions due to the relative motions of three large tectonic plates (the Pacific Plate, the Cocos Plate and the North American Plate) in the region. The relatively dense oceanic crust of the pacific plate is subducting beneath the Mexican landmass. This motion can result in large earthquakes such as today’s event. The interaction of the subducting plate and the mantel rock beneath the Mexican landmass also results in volcanism in the area.

The earthquake was recorded at seismic stations worldwide, including stations of the Irish Nation Seismic Network (INSN), see seismic waveforms below (select figure to enlarge).

Further information is available from the following sources:

https://earthquake.usgs.gov/earthquakes/eventpage/us6000ah9t/executive?utm_medium=email&utm_source=ENS&utm_campaign=realtime

https://www.emsc-csem.org/Earthquake/earthquake.php?id=870434

 

2020-06-18, M7.4, Kermadec Islands

At 12:49:53 on the 18th of June 2020, an earthquake of magnitude 7.4 struck in the Kermadec Islands region of the South Pacific (see map below). The earthquake occurred at a depth of 8 km, locating approximately 650 km northeast of New Zealand’s North Island. This region of the Tonga-Kermadec subduction zone experiences high levels of seismic activity, with nearly 20 events of M 6.5+ over the past half century within 250 km the 18th of June earthquake.

The earthquake was recorded at seismic stations worldwide, including stations of the Irish National Seismic Network (INSN), see seismic waveforms below (select figure to enlarge).

Further information is available from the following sources:

https://www.emsc-csem.org/Earthquake/earthquake.php?id=868826

https://earthquake.usgs.gov/earthquakes/eventpage/us6000ae4n/executive

2020-06-03, M6.8, Chile

At 07:35:33 UTC (03:35:33 local time) on the 3rd of June 2020 a magnitude 6.8 earthquake struck northern Chile (see map below). The earthquake occurred at a depth of 87 km, locating approximately 200 km east of the city of Antofagasta. Chile experiences very high rates of seismic activity due to its location along the boundary of the Nazca and South American tectonic plates. In addition, the depths at which earthquakes occur in Chile varies greatly, with shallower events occurring along the coast in the west, and deeper events occurring in the east. The largest earthquake recorded in the modern era of instrumental seismology, the M9.5 Valdivia earthquake, occurred in southern Chile in 1960.

The earthquake was recorded at seismic stations worldwide, including stations of the Irish National Seismic Network (INSN), see seismic waveforms below (select figure to enlarge).

Further information is available from the following sources:

https://www.emsc-csem.org/Earthquake/earthquake.php?id=864463

https://earthquake.usgs.gov/earthquakes/eventpage/us6000a4yi/executive

2020-05-15, M6.5, Nevada, USA

At 11:03:28.6 UTC on the 15th of May 2020 a magnitude 6.5 earthquake struck western Nevada, USA (see map below). The earthquake occurred at a depth of 10 km, locating approximately halfway between the cities of Reno and Las Vegas. The earthquake has been felt in the states of Nevada, California and Utah by members of the public. According to the United States Geological Survey (USGS), about two dozen M5+ earthquakes have occurred within 100 km of this event over the past 50 years.

The earthquake was recorded at seismic stations worldwide, including stations of the Irish National Seismic Network (INSN), see seismic waveforms below (select figure to enlarge).

Further information is available from the following sources:

https://www.emsc-csem.org/Earthquake/earthquake.php?id=857265

https://earthquake.usgs.gov/earthquakes/eventpage/nn00725272/executive

2020-05-14, M0.6, Irish Sea

On the 14th of May 2020 at 03:52:54 UTC, an earthquake of magnitude M0.6 occurred in the Irish Sea. The earthquake located approximately 20km east of the Isle of Man, and occurred at a depth of 3km. The epicentre location is indicated with a red circle in the map below, black lines denote major fault zones in and around Ireland. Events of this nature are not uncommon in the Irish Sea, with several small events (M < 1.1) detected near the Isle of Man in the past 5 years.

The event was recorded by the Irish National Seismic Network (INSN) and British Geological Survey (BGS) seismometers, for seismograms see the plot below (click image to enlarge).

 

2020-05-02, M6.6, Crete, Greece

At 12:51:05.6 UTC on the 2nd of May 2020 a magnitude 6.6 earthquake struck 100 km south of the Greek island of Crete (see map below). The earthquake occurred at a depth of 10 km and was widely felt on the island of Crete. Several aftershocks up to M5.4 occurred in the space of a four hours after the initial shock. No casualties have been reported at the time of writing.

The earthquake was recorded at seismic stations worldwide, including stations of the Irish National Seismic Network (INSN), see seismic waveforms below (select figure to enlarge).

Further information is available from the following sources:

https://www.emsc-csem.org/Earthquake/earthquake.php?id=853296

https://earthquake.usgs.gov/earthquakes/eventpage/us700098qd/executive

2020-04-25, M0.9, Irish Sea

On the 25th of April 2020 at 04:11:52 GMT, a magnitude M0.9 earthquake occurred in the Irish Sea approximately 15km off the English coast north of Blackpool. The epicentre location is indicated with a red circle in the map below, black lines denote major fault zones in and around Ireland. Events of this nature are not uncommon in the Irish Sea, a similar event with magnitude M1.7 occurred nearby on the 16th December 2019.

Seismic noise changes during Covid19

Instruments operated by the INSN track ground motions from natural phenomena, such as earthquakes, but also human-made ground vibrations, so-called ‘seismic noise’. After the lockdown started on the 28th March 2020, some INSN stations detected seismic noise levels significantly lower than before the lockdown. See figure below for seismic noise data from our station located in the Dublin mountains (click figure to enlarge).


Frequently Asked Questions:

What are seismometers for?
Seismometers respond to ground motion and are traditionally used to detect and locate earthquakes. The earthquake information in turn is used by seismologists and geologists to study the Earth’s interior.

What is seismic noise?
Seismic noise is a relatively persistent ground vibration that is not caused by earthquakes (Note: it is not a vibration in the air). Seismologist termed these signals ‘noise’ because they are a nuisance when trying to detect small earthquakes. Seismic noise has very low amplitude and cannot be felt by humans.

What can a seismometer not tell?
Seismometers do not distinguish between human made seismic noise, naturally made seismic noise (e.g. by strong wind) or seismic waves caused by an earthquake. Seismometers simply record ground vibrations no matter what caused them.

How do you know that the seismic noise is made by human activity?
Seismic noise can be caused by human activities like industrial works (e.g. large building sites, quarries, tunnelling),  road traffic, rail traffic, airports, but it is also caused by natural phenomena like for example wind or water flow in a river. Human induced seismic noise is readily identified by its clear variation between day and night and also lower amplitudes on weekends.

Why does the diagram above stop at Sunday April 26th?
After Sunday 26th April 2020 seismic noise recorded at this station is dominated by more local noise sources (likely related to site machinery) and therefore it no longer gives an average regional picture.

Does human induced seismic noise originate just from traffic?
No. Large building sites, quarries, tunnelling, road traffic, rail traffic and airports are some other examples of sources for human induced seismic noise.

How far away can the vibrations still be detected?
This depends on the type of vibration source, more specifically on the strength and the frequency of the vibration causing the seismic noise waves. It is not possible to determine source distances or locations with a single station, but the spectral content of the data may indicate if the source is near or far. As an approximate guideline here are some numbers: Depending on rock type seismic noise originating from heavy industry can be detected up to distances of (approximately) 25km; from railways up to 15km; from motorways up to 6km; and from smaller roads up to 1km (International Handbook of Earthquake and Engineering Seismology, Part A, 2002, Edited by William H.K. Lee, Hiroo Kanamori, Paul C. Jennings, Carl Kisslinger, ISBN-10: 0124406521, ISBN-13: 978-0124406520).

How do you know its not a disturbance right beside the station?
Disturbances right beside a station show as very large amplitudes and don’t follow the smooth day/night variation that is observed for human induced noise from further afield.

Is this only seen in Ireland?
No. The effect of lockdown measures is observed at seismic stations worldwide, though only stations in or near urbanized areas show the effect, see for example https://www.nationalgeographic.com/science/2020/04/coronavirus-is-quieting-the-world-seismic-data-shows

Can you see this noise change all over Ireland?
No. Most of the seismic stations in Ireland operate at remote locations, away from urban areas, making them less sensitive to human induced seismic noise.

Why are seismologists interested in seismic noise?
In the 1990s methods were developed to derive ground properties from seismic noise data. In addition noise data are now widely used to monitor natural processes, for example ocean wave state, volcano activity and water flow at inaccessible locations like in caves and glaciers.


On the 10th April 2020 Martin Möllhoff gave this interview about seismic ground vibrations on Tipp FM:

 

 

 

2020-03-25, M7.5, Russia

At 02:49:21 GMT on March 25th 2020 a magnitude M7.5 earthquake struck to the east of the Kuril Islands, Russia (see map below). The earthquake occurred at a depth of 56.7 km and the NSW Pacific Tsunami Warning Center have said that there is no threat of a tsunami as sea-level readings from the nearest two deep ocean dart gauges confirm only small tsunami waves were generated.

The earthquake was recorded at seismic stations worldwide, including stations of the Irish National Seismic Network (INSN), see seismic waveforms below (select figure to enlarge).

Further information is available from the following sources:

https://earthquake.usgs.gov/earthquakes/eventpage/us70008fi4/region-info

https://www.emsc-csem.org/Earthquake/earthquake.php?id=841592

2020-03-22, M5.4, Zagreb, Croatia

At 05:24:02 (UTC) on the 22nd of March 2020, a M5.4 earthquake struck 7km northeast of Zagreb, Croatia. The earthquake occurred at a depth of 10km and caused several injuries as well as widespread damage to buildings in Zagreb. This event is the largest to occur near Zagreb in the past 140 years.

The earthquake was recorded at seismic stations worldwide, including stations of the Irish National Seismic Network (INSN), see seismic waveforms below (select figure to enlarge).

Further information is available through the links below:

https://www.emsc-csem.org/Earthquake/earthquake.php?id=840695

https://earthquake.usgs.gov/earthquakes/eventpage/us70008dx7/executive

Live Seismograms
All stations here
Filtered versions here
DSB - Dublin
VAL - Kerry