Institute of Geophysics AS CR, v. v. i.

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West Bohemia seismic network WEBNET

 

Monitoring the seismic activity of the West Bohemia/Vogtland earthquake swarms


For information about the recent seismic activity please follow the link above!



August 2011: New swarm activity in Novy Kostel
The activity started in the evening of 23 August. Actual information about the evolution of EQ swarm you can find here.
The location of hypocenters directly below the NKC station, so it appears a new patch of the fault plane is being activated - see the joint plot pf all activity in NK area - the recent events are indicated in dark red.
 Deph section of hypocenters in the Novy Kostel area; the location of the recet swarm indicated by ellipse.The first day of the swarm recorded at NKC

Since 6th till 13th October 2008 more than 10 000 (!!) events occurred at the southerm edge of the Nový Kostel area. The hypocenters lie in the depth range 10.5 to 9 km (below the microswarm of February 2007) and have reactivated the southerm patch of the 2000 swarm. Several M>3.5 events have occurred making this swarm the strongest one since the M=4.6 swarm of 1985/86.

The swarm is exceptional by the unusually fast release of energy
(>10 000 events in 7 days). Due to this evolution the activity is expected to continue in next days/weeks with possible interrupts.




February 2007: "Fast" micro-swarm in the Nový Kostel area
Since 9th till 10th February June almost 1500 (!) microearthquakes in the magnitude range -0.5 .. 1.8 occurred at the southerm edge of the Nový Kostel area. The hypocenters have reactivated the southerm patch of the 2000 swarm activity.

The seismicity shows very fast evolution with plenty of overlapping events and unusually small interevent times. See figure showing all the post-2000 swarm activity with color-coded microswarms.




June 2005: New micro-swarm activity in the Nový Kostel area
Since 15th June more than 100 microearthquakes in the magnitude range -0.5 .. 1.1 occurred in the Nový Kostel area. The hypocenters are located close to the first events of the 2000 swarm with an offset of 500 m westwards. See figure showing all the activity in the NK area during the past 15 years.

The temporal statistics of the activity, which is partially similar to that of the 1997 and 2000 swarms, indicates a possible increase of activity in the next weeks.



22-Feb-2004: Deep micro-swarm in the Nový Kostel area
Between 00:44 A.M. and 4:45 P.M. around 50 microearthquakes in the magnitude range -0.5 .. 1.3 occurred in the Nový Kostel area. The new micro-swarm displays several anomalous features:
  • most of the earthquakes belong to elongate cluster in the depth of 13.5 km
  • the strike of the cluster (approx. -30°) differs from that of the main fault plane (-11°)
  • in the map view the cluster lies 2 km apart from the main fault plane to west
  • the preliminary focal mechanisms show dip-slip regime



WEBNET: a local seismic network monitoring the NW-Bohemia earthquake swarm activity
  • a local seismic network for monitoring the West-Bohemian earthquake swarm activity
  • established in 1994, still being upgraded
  • now (year 2002) it consists of 9 digital stations NKC, KRC, LBC, SKC, KOC, LAC, STC, VAC, TRC
  • equipment: four Lennartz PCM 5800 telemetry stations, four Mars-88 RC, one Mars-88 FD
  • recent upgrade: Mars-88 being replaced by Nanometrics Callisto network using Orinoco Wavelan network
  • data transmission: Internet connection between the data centre on TV tower Zelená Hora and Prague GI
  • a common project of the Geophysical Institute and the Institute of Rock Structure and Mechanics of the Czech Academy of Sciences

Click map



Seismic activity in the whole NW-Bohemia/Vogtland region
Occurrence of microearthquakes in the swarm area is clustered in space and time. The space distribution of the epicentres is obvious from the figure showing the microearthquakes occurred in the period 1991 - 1997. The epicentres in particular epicentral zones are distinguished using different colours.



Nový Kostel area
The Nový Kostel area dominates the recent seismicity of the whole region. The figure depicts the space-time clustering of microearthquakes in the period 1991 - 1997. It is evident the foci tend to cluster in space, and the individual swarms took place in narrow volumes. An important feature of the spatial distribution of the hypocentres is the lamella-like character of the focal belt evident form the horizontal projection (upper left). The January 1997 swarm is shown in detail.
The picture of seismic energy release changed after occurrence of the 2000 swarm and obtaining accurate relative locations of the 1985/86 swarm. As is indicated in the figure, the major part of the ectivity takes place close to a steeply dipping almost N-S oriented fault plane.
Try the 3D view of the earthquakes in the Novy Kostel area. It displays a 3-dimensional view of the hypocentres occurred in this epicentral area witihn the period 1991-2001.
HELP: rotate the image by dragging by mouse; zoom the image by Shift+drag mouse up/down.

The animation was created using the Java applet LiveGraphics 3D by Martin Kraus and it works with IE 5.0 and later only.



January 1997 Ml 3.0 swarm
The January 1997 swarm was the best ever recorded seismic sequence in the West-Bohemia/Vogtland region thanks to the WEBNET network. It occurred in the Nový Kostel area in the period from January, 11 to January 28, 1997 when more than 1500 microearthquakes in the magnitude range from -2.0 to 3.0 were recorded. The focal area of the swarm shows a corner-like shape dipping to East.
A combination of the waveform type analysis and full moment tensor determination enabled more than 700 events to be classified following their focal mechanism. Totally eight source mechanism types were identified differing both in their fault plane solution angles and in percentage of DC component. The figures show spatial distribution of particular event types and representative source mechanisms corresponding to eight multiplet groups.
The occurrence of particular foci mechanisms was not random. In the first phase of the swarm the normal movements (red foci) dominated, while in the second phase the reverse events with higher volumetric components (blue foci) prevailed. The attached animation shows the temporal development of the swarm.



Active people behind WEBNET Former members of WEBNET group
  • Frantisek Hampl (+1997) - founder of most of stations
  • Pavel Kratochvil (student) - web design, data processing
  • Jiri Soukup - station & network maintenance




Send comments to Tomas Fischer, tomfis AT ig.cas.cz

Last update 2011-Aug-25