Detection and Identification of Near Seismic Events by SeisComP3 limited by a sparse distributed Seismic Network Thomas Burghardt, Friedrich-Schiller- Universität Jena 17. Januar 2013 User Group Meeting Potsdam GFZ

Contents Configuration of the network Which signals are measured and which features the measurement has Examples for detected events The reported events Conclusion

How TSN and SX network is configured for SeisComP3?

The outer stations stabilize the localization of regional, Mediterranean and teleseismic events

The inner Stations are for the detection of the local events

Grid Search Algorithm Parameter

The outer domain for Grid Search is the ^default configuration of SC3

The inner Grid Search has a dense grid point domain of R=0,0625° ca Grid Points are investigated

Which signals the network measures?

Local blasts Local blasts or mining in Poland or northwest Germany Local blasts at Bavaria Teleseismic Events Mediterranean, Balcan Local earthquakes or mining events

The ambiguity of the Grid Search Algorithm and of LocSAT

Conclusion: There are different detection and location results at two computers with the same SC3 configuration. To my mind the cause depends on the not stabilized Grid Search Algorithm for near events and on the difficulties of LocSAT to localize teleseismic events with a regional velocity model.

Is the localization error less for a denser distribution of the stations in the network ?

Is answer seems to be no. Probably the influence of the S onsets and the unsufficient pick order provided by the Grid Search have a great portion to the false localization

Examples P- und S Onsets

Gräfenberg, Germany 05. Apr. 2012, blast SHM: 49,651 ; 11,406, ML=1,7 S2: 49,84 ; 11,85 Neustadt am Kulm S1: 47,62 ; 12,82 Ramsau, Oberbayern wrong distant station TRPA (HU)

Where is the array?

Swabian Alp, Albstadt, Germany, Earthquake 02. Jan :55 EMSC: 48,24 ; 9,01 ML=2,3 S2: south. Nürnberg: 49,16 ; 10,91 P Onsets, BFO is absent, but the pick exists S1: S Onsets Near Cannes after relocation after put out of the far station: TRPA : 42,97 ; 6,03

S2: Grid Search takes the P Onsets

S1: Grid Search collects the S Onsets

S2: south Nürnberg, P-OnsetsS1: Near Cannes, S-Onsets

S2: vp=6,18 ; vpk=6,97km/s S1: vp=5,15 ; vpk=8,06 km/s In spite of S Onsets vpk: velocity of LocSAT after determination the hypocenter

Freiburg/Breisgau, Germany, Earthquake 01. Jan :48 EMSC: 48,37 ; 8,99 ML=2,1 S2: 48,30 ; 8,64 P Onsets S1: 48,30 ; 8,63 P Onsets

The Station BFO near of Epicenter stabilized the Location vp=6,89, vpk=7,38km/s, Res. of BFO: -0,1

Only some grid cells take part for location?

Plauen, Germany, Earthquake 28. Dec :55 SHM: 50,454 ; 12,225, ML=1,1,10,5km S2: 50,46 ; 12,34 MLv=1,1 S1: 50,45 ; 12,33 MLv=1,1 The best place for determination of hypocenter, because of the dense network

The nearest station PLN is too far from epicenter

The right location by manually picking and location

Regression line for manual Picks vp=6,64km/s S1: Automatic Regression line vp=4,32, vpk=6,37km/s The automatical onsets are spreading much

Legnica, Poland, 03. Jan. 2013, 22:25, mining event, EMSC: 51,39 ; 16,28 ML=2,9 S2: 52,03 ; 19,77 P Onsets S1: 48,73 ; 18,40 S Onsets

P Onsets => 52,03 ; 19,77

The emergent onsets are spreading much vp=7,36km/s, dev.fitting: 2,67s, bad location

False Station SMOL, S Onsets for network stations: 48,73 ; 18,4

Manually location by SHM, only with the S Onset of nearest Station the result is comparable to EMSC: 51,495 ; 15,904

Novy Kostel, Czech, 07. Jan. 2013, 17:19 Earthquake SHM: 50,231 ; 12,452, ML=1,8 S2: 50,24 ; 12,45 ML=1,9 S1: 50,23 ; 12,47 ML=1,9

LocSAT gives some too high velocity: vpk=6,99km/s, vp=5,8km/s

The errors show the high velocity location, the S Onsets are shown clearly.

By the waveform the local earthquake is recognized distinctly

A near blast at Most has another waveform

The spectra of earthquake has a max. At 20 Hz, in contrast to 4 Hz for the blast Novy Kostel, Earthquake Most, Blast

The regression line of Onsets are suitable for identifcation teleseismic events Honshu, 29. Dec. 2012, 23:05 EMSC: 37,11, 141,15 S2: 50,74 ; 13,67 187km s1: 50,85 ; 13,73 after removing Station SOP: 52,96 ; 17,00

Vp=20,29, vpk=20,57km/s before the removing SOP, the last station

Vanuatu, 22. Dec. 2012, 07:53 EMSC: -20,28 ; 169,6, mb=4,9 only s1: 51,02 ;11,21 (near Weimar, Germany)

TT is bent, therefore the location shows to Thuringia and not to Poland, the regression line gives vp=32,9, vpk=14,9km/s

The determination of S velocity by regression line is problematical because of the wrong epicenter resulting by S Onset location

Detection Results of the reported events to the Office of Environment and Geology of Thuringia

The detectibility of the network in the swarm and in the tectonic region is sufficiently good. Down up to ML=1,5 with a location error up to 15 km the network give hints for manually revising. At the mining areas due to the sparse distribution of stations the Magnitude threshold is higher than 2.

Conclusion To my mind the Grid Search Algorithm has to be tuned to the sparse network to achieve a better location and less ambiguity. It will not become perfectly, because of the heterogeneity and the missing of coherence of signals in comparison to the teleseimic signals. With the absent regonizability of S onsets arises a big problem for localization. At this level of development in the local event detection with a sparse network, SC3 is an excellent tool for detection of the events, but a revision by a seismologist is absolutely necessary. The possibility to determine the spectra of the event with SC3 tool would be helpful.