Rapid magnitude determination for Vrancea early warning system and the April 25, 2009 Ms= 5.3 event (A. Marmureanu, C. Ionescu, Gh. Marmureanu)

The Romanian territory is exposed to high seismic risk associated to earthquakes occurring in Vrancea area. Major earthquakes occurred in this area in the last century: November 10, 1940, Mw=7.7, depth 150 Km; March 4,1977, Mw=7.4, depth 95 Km; August 30, 1986, Mw=7.1, depth 130 Km and May 30, 1990, Mw=6.9, depth 90 Km. The metropolitan area of Bucharest has a population of 2.6 million people. Bucharest is the 6th largest city in the European Union by population within city limits. Bucharest is one of the European cities with very high seismic risk

Location of earthquakes used in this study together with the location of the stations from the epicentre (VRI,MLR,PLOR). (16183 waveforms ~3000 events).

Offline applications used to tune up different algorithms

Magnitude estimation absolute error (for al records and all three stations).

Real time acquisition Permits processing of offline continuous data recorded since 2004 until now via mseed2ring

Detection voting scheme (our detector – a modified STA/LTA detector) VRI – Vel E VRI – Vel N VRI – Vel Z PLOR – Vel E PLOR – Vel N PLOR – Vel Z MLR – Vel E MLR – Vel N MLR – Vel Z 3 votes 9 votes Magnitude computation Time window

VRI – Acc Z 9 votes PLOR– Acc Z MLR – Acc Z M VRI M PLOR M MLR Votes on magnitude (it is decided if a final one is computed) M=(M MLR +M PLOR +M VRI )/3 Magnitude computation

Magnitude estimation absolute error (left)(for al records). Magnitude absolute errors averaged (right) (if the earthquake is recorded on all three stations, the final magnitude is the average of all local magnitudes)

April 25, 2009 Ms= 5.3 event This event was correctly detected by the early warning system and a magnitude was computed in the first 5 seconds. The magnitude was overestimated with 0.22 magnitude degrees.