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Automated Processing of Earthquake Swarm Records at Very Short Epicentral Distances

Automated Processing of Earthquake Swarm Records at Very Short Epicentral Distances. José M. Cepeda Universidad Centroamericana, (UCA) San Salvador, El Salvador. Outline. Introduction Strong Motion Networks in El Salvador Cases of Application Procedure for Swarm Records Purpose

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Automated Processing of Earthquake Swarm Records at Very Short Epicentral Distances

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  1. Automated Processing of Earthquake Swarm Records at Very Short Epicentral Distances José M. Cepeda Universidad Centroamericana, (UCA) San Salvador, El Salvador

  2. Outline • Introduction • Strong Motion Networks in El Salvador • Cases of Application • Procedure for Swarm Records • Purpose • General Procedure • Calculation of Trace Envelope • Illustration of Procedure • Routine processing procedure • Availability of data • Future activities. Automated Processing of Earthquake Swarm Records… J. Cepeda – Cosmos Workshop

  3. 1. Introduction • Pacific Coast in Northern Central America • Subduction earthquakes (Cocos – Caribbean plate boundary) • Volcanic chain earthquakes • 21,000 km2 Automated Processing of Earthquake Swarm Records… J. Cepeda – Cosmos Workshop

  4. 1. Introduction • Subduction vrs Volcanic Chain Earthquakes • Differences in duration • Definition of PET in instruments • Long pre-event durations in Volcanic Chain Earthquakes Automated Processing of Earthquake Swarm Records… J. Cepeda – Cosmos Workshop

  5. 1. Introduction • Swarms in Volcanic Chain Earthquakes • Period 1985-1999 • 10 significant swarms • Records of 14,000+ Earthquakes • Long pre-event portions • Multiple events in single record Automated Processing of Earthquake Swarm Records… J. Cepeda – Cosmos Workshop

  6. 2. Networks in El Salvador • Owner institutions: • Universidad Centroamericana (UCA) • Servicio Nacional de Estudios Territoriales (SNET) • Hydroelectrical Power Company (CEL) • Geothermal Power Company (LAGEO) • 48 digital instruments (1 instrument / 440 km2) • SSA-2: 25% • QDR: 21% • Etna: 35% • K-2: 19% Automated Processing of Earthquake Swarm Records… J. Cepeda – Cosmos Workshop

  7. 2. Networks in El Salvador • West (19%) – Central (57%) – East (24%) • North (19%) – Volcanic chain (69%) – South (12%) Automated Processing of Earthquake Swarm Records… J. Cepeda – Cosmos Workshop

  8. 2. Networks in El Salvador • Strong motion recording since 1951. • First digital recordings: 1996. • Networks fully digital since 2002. • Pre-event memory: 10.24 s • Post-event running time: 15 s • Trigger levels: • 0.01 g horizontal, 0.005 g vertical. Automated Processing of Earthquake Swarm Records… J. Cepeda – Cosmos Workshop

  9. 2. Networks in El Salvador • Total of Strong Motion Records: 1323 • 12% from analogue instruments (Montana and SMA-1). • 88% from digital instruments (SSA-2, Etna, K2 and QDR). • Important earthquakes recorded: • 19/Jun/1982 (MS 7.3 subduction) – 1 record. • 10/Oct/1986 (MS 5.4 shallow upper crustal) – 6 records. • 13/Jan/2001 (MS 7.8 subduction) – 26 records. • 13/Feb/2001 (MS 6.5 shallow upper crustal) – 21 records. • Largest PGA recorded: 1.1 g (13/Jan/2001, 61 km rupture distance). Automated Processing of Earthquake Swarm Records… J. Cepeda – Cosmos Workshop

  10. 3. Cases of Application • Attenuation equations. • Backanalysis of liquefaction phenomena. • Observation of rupture directivity. • Monitoring of instrumented slopes. • Seismic risk scenarios. Automated Processing of Earthquake Swarm Records… J. Cepeda – Cosmos Workshop

  11. 4. Procedure for swarm records • Purpose • General procedure • Calculation of trace envelope • Illustration of procedure Automated Processing of Earthquake Swarm Records… J. Cepeda – Cosmos Workshop

  12. 4. Procedure for swarm records Purpose • Routine for the preliminary batch processing of swarm earthquake records. • Cut large pre-event portions. • Extract traces of multiple events contained in a single record. Automated Processing of Earthquake Swarm Records… J. Cepeda – Cosmos Workshop

  13. 4. Procedure for swarm records General procedure • SSA or EVT file  ASCII file. • Select vertical component. • Obtain ‘smoothed’ envelope of record and amplitude of envelope. • Obtain ‘crests’ in amplitude of envelope. • Obtain ‘valleys’ and ‘plains’ in amplitude of envelope. • Find values of time for lowest ‘valleys’ and ‘plains’ preceding ‘crests’. • Values of time in step (6) are cutting points. Automated Processing of Earthquake Swarm Records… J. Cepeda – Cosmos Workshop

  14. 4. Procedure for swarm records Calculation of trace envelope • Baseline correction (mean of record). • Obtain First and second derivative of record. • Identify flat portions (1st derivative is zero), local peaks (change of sign in 1st derivative) and identify maximum and minimum (sign of 2nd derivative). Automated Processing of Earthquake Swarm Records… J. Cepeda – Cosmos Workshop

  15. 4. Procedure for swarm records Calculation of trace envelope 4) Create vectors of maximum and minimum values. • ‘Smoothing’ of envelope: divide record in segments of width ‘deltat’ and select peaks of vectors in (4) within each segment. • Interpolate envelope to a fixed and uniform time step. • Calculate amplitude of envelope. Automated Processing of Earthquake Swarm Records… J. Cepeda – Cosmos Workshop

  16. Illustration of procedure Date: 2001/May/8 Time: 18:04 Magnitude: 3.6 ML Depth: 8.2 km Epicentral distance: 9.3 km Station: HSGT (San Vicente, El Salvador) Automated Processing of Earthquake Swarm Records… J. Cepeda – Cosmos Workshop

  17. 5. Routine processing (SSA-2). • SWS by Kinemetrics (preliminary batch processing). • SSA to DAT. • DAT to V1. • V1 to V2 (0.12 – 45 Hz). • V2 to V3 (-std option for calculation of SA). Automated Processing of Earthquake Swarm Records… J. Cepeda – Cosmos Workshop

  18. 5. Routine processing (SSA-2). • Strong Motion Analyst by Kinemetrics (Record by record) • Conversion SSA to EVT format. • Conversion EVT to V1 unprocessed format. • V1 to V2 processing: • Baseline and instrument correction. • High pass filtering of velocity and displacement. • Option: Shakal and Ragsdale (1984) method. • Corner frequencies: [0.12-0.20] Hz and 45 Hz (criteria: velocity & displacement time histories). • V2 to V3 (Fourier & response spectra). Automated Processing of Earthquake Swarm Records… J. Cepeda – Cosmos Workshop

  19. 6. Availability of data. • www.uca.edu.sv/investigacion/terremoto/indice.htm (MS 7.8 - 13/Jan/2001, MS 6.5 - 13/Feb/2001, MW 5.1 - 17/Feb/2001). • db.cosmos-eq.org/scripts/earthquakes.plx#CAM (MS 7.8 - 13/Jan/2001, MS 6.5 - 13/Feb/2001, MW 5.1 - 17/Feb/2001). • www.snet.gob.sv/Geologia/Sismologia/13%20de%20febrero/13%20de%20febrero.htm (MS 6.5- 13/Feb/2001) • nsmp.wr.usgs.gov/data_sets/20010113_1.html (MS 7.8 - 13/Jan/2001) • nsmp.wr.usgs.gov/data2/cdrom_sm_1933-1986/1986/1986.zip(MS 5.4 - 10/Oct/1986) Automated Processing of Earthquake Swarm Records… J. Cepeda – Cosmos Workshop

  20. 7. Future activities. • More QDRs and Etnas. • Modem connection to SSA-2. • Installation of instruments in Guatemala (near the Motagua Fault) and Managua, Nicaragua. • Availability of the full UCA data set in the Internet. Automated Processing of Earthquake Swarm Records… J. Cepeda – Cosmos Workshop

  21. Thank you

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