Damaging Earthquake Hits Groningen, Netherlands

M2.8, 9KM NORTH-EAST OF GRONINGEN, NETHERLANDS,11:42 UTC.

A minor magnitude 2.8 earthquake strikes Groningen, causing minor damage.

A magnitude 2.8 earthquake struck about 9 kilometres (5.7 miles) north-east of Groningen, Netherlands. The city of 180,000 people was badly shaken by the minor tremor, a very frequent event that the people of Groningen are having to get used to.

The Netherlands is not renowned for its tectonic seismic activity, but in the north-east of the country near Groningen there exists an extensive gas field which has kept the country's economy afloat for nearly two decades. This gas field has led to numerous minor tremors since 1996, including earthquakes up to magnitude 3.6 (16th August 2012), and over time these earthquakes have caused minor damage to building interiors, interior walls and structural walls of many new and old buildings within Groningen city and its surrounding villages and towns.

The issue of this induced seismic activity has brought Royal Dutch Shell into direct confrontation with the populace of Groningen, many of whom have suffered uninsured damages to their properties. This earthquake has been no different (see below). The government is reluctant to reduce gas extraction levels as the taxes from the extraction is keeping the Dutch economy healthy and alleviated the sorts of problems that larger economies in Europe, such as Ireland, Italy, Spain & Portugal, faced during the Financial Meltdown of 2008-09.

Magnitude & location parameters:

KNMI (Royal Dutch Meteorological Institute):
M2.8, 53.271N, 6.673E, 3km depth

KNMI are a local seismic agency whose location and magnitude parameters will prove highly accurate for quakes within the Netherlands. They are highly reliable in this instance.

GEOFON (Potsdam):
M3.1, 53.35N, 6.40E, 3km depth

GEOFON are a teleseismic agency whose location and magnitude parameters will prove unreliable due to the scarcity of local data sources within the Netherlands or neighbouring Germany. They are less reliable than KNMI in this instance.

Images of damage:
https://pbs.twimg.com/media/Byx3_WOCcAA-wyG.jpg
https://pbs.twimg.com/media/Byx-JC6IIAATZnC.jpg

Minor earthquake strikes northern North Sea

M2.8, NORTH SEA, EAST OF WICK, SCOTLAND, 10:59AM BST.

Minor earthquake strikes northern North Sea, probably within oil-rich graben region.

This earthquake struck at 10:59 am in the North Sea, about 275 kilometres east of Wick, and 240 kilometres west of Stavenger, Norway. This was probably caused by a normal fault in the graben areas common in the northern North Sea, where extensive oil deposits are accessible.

These sorts of events are relatively common. The last one of size occurred in late July, east of the Humber estuary (M3.0, 27/7/14). They very rarely exceed magnitude 3, but some, such as the Dogger Bank Earthquake of 1931 can cause minor damage and exceed magnitude 6.

Pongaroa Earthquake Rattles New Zealand

MAGNITUDE 5.5, 15KM WEST OF PONGAROA, NEW ZEALAND. 23RD SEPTEMBER, 2:41 AM NZST.

Sizable earthquake strikes lower North Island, waking thousands in the early hours.

This earthquake is likely a triggered event from the Eketahuna earthquake on 20th January (Mw 6.2), on a parallel fault due east from the Eketahuna earthquake. This quake is unlikely to cause damage to the main towns (Eketahuna, Masterton, etc.), but may have caused minor damage in the a very localised region. Reports so far suggest that the quake caused no damage, which is quite lucky. The quake gained over 3300 felt reports and a maximum intensity of MM7 (lightly damaging shaking).

This earthquake had a foreshock of M3.8 at 12:06 am NZST (which gained 95 felt reports and a maximum intensity of MM4 (light shaking)); as of 6:30 pm NZST has had two aftershocks of significance; an M3.7 at 3:42 pm NZST, followed by an M3.0 at 3:47 pm NZST. The M3.7 gained 48 felt reports and a maximum intensity of MM5 (moderate shaking).

Recent research released by GNS suggests that the Kapiti slow-slip event which began in mid-2013 may have loaded stresses in the area of Eketahuna & today's Pongaroa quakes. This can be supported by recent seismic activity offshore of Paraparaumu which suggest the slow-slip event has still not fully subsided, or may have restarted with a very short recurrence interval.

NZ Herald Report: http://www.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=11329696

GeoNet summary:http://geonet.org.nz/quakes/region/newzealand/2014p715167

GNS research on Kapiti slow-slip event & links with Eketahuna:http://info.geonet.org.nz/display/quake/2014/05/15/New+Zealand's+'silent+earthquakes'+of+2013

Written by J H Gurney on the 23rd September.

Moderate Earthquake Rattles Sweden

Southern Sweden Shaken By Tremor

Magnitude 4.7, near Aelvdalen, Western Sweden.

A moderate earthquake struck near the small Swedish town of Aelvdalen on Monday 15th September. The earthquake was reportedly felt throughout most of Sweden, as well as neighbouring Norway and Finland. There are reports of minor damage.

The magnitude 4.7 earthquake struck at 3:08pm local time, and had a focal depth of 14.3 kilometres. Within a fifty mile radius there have been no recorded earthquakes over magnitude 4.0 since 1970; in fact there have been only nine earthquakes over magnitude 4.0 since 1970 in Sweden, the largest a magnitude 4.8 earthquake in the south of the country in July 1986.

Earthquakes of this kind are incredibly rare; although Sweden has minor seismic activity (75 earthquakes since 1983 over magnitude 3), most of these earthquakes are either coastal (near Gothenberg and Malmo in the south of the country) or near Gallivare in the north of the country (caused by deep mining for iron, copper, silver and gold). Today's earthquake was located deep inland in the mountainous regions of western Sweden, where the last recorded earthquake of size was in 1497.

Scandinavia may not seem to be of huge consequence to us in the UK, but earthquakes near Norway are believed to have triggered tsunamis in the past (for example, the Storegga Slide of 8000 years ago). Similar events are indeed possible, though it is incredibly unlikely they will occur during our lifetimes.

Earthquake Parameters

GEOFON (GFZ Potsdam, Germany)

Body-wave magnitude: 4.7

Depth: 10 kilometres

Epicentre: 61.56N, 14.49E

USGS

Body-wave magnitude: 4.7

Depth: 14.3 kilometres

Epicentre: 61.535N, 14.390E

NORSAR

Magnitude: 4.68

Epicentre: 61.77N, 14.10E

This article was written on the 15th September 2014 by J H Gurney.

Mining Earthquake in Yorkshire

Mining Earthquake in Yorkshire

Magnitude 1.9, near Hensall, North Yorkshire

A minor earthquake struck near the North Yorkshire village of Hensall on Thursday 11th September. The earthquake was reportedly felt in the nearby villages of Hensall, Kellington, Little Heck and Gowdall. There was no damage.

The magnitude 1.9 earthquake struck at 11:31pm, and had a focal depth of about 1 kilometre. Previous seismicity has been recorded in this locality, with nine earthquakes occurring within ten miles of today's earthquake in the last four years. These include a magnitude 2.0 quake in June 2010 and a magnitude 2.1 in February last year. The latter tremor gained an article in the Selby Times.

Earthquakes of this size are commonplace in regions that underwent mining activity in the past, and are often at shallow depths (max. 5km). Similar earthquakes have been occurring over the past year near New Ollerton, Nottinghamshire, and this earthquake was of the same nature. Old mine works, having been abandoned, lead to stress changes within the surrounding rock, which can cause minor earthquakes and on occasion subsidence of overlying land. 

Similar events occur abroad in Germany, Lower Silesia in Poland and northwestern Bosnia-Herzegovina, where a minor magnitude 3.5 earthquake killed five miners in a collapse this Monday. However, in Britain mining earthquakes generally do not exceed magnitude 2.0. With the abandonment of most mines where these earthquakes occur, there is very low risk for any of the public due to these quakes in the UK.

This article was written on the 12th September 2014 by J H Gurney.