Automated Processing of Earthquake Swarm Records at Very Short Epicentral Distances José M. Cepeda Universidad Centroamericana, (UCA) San Salvador, El Salvador 1
Outline 1) Introduction 2) Strong Motion Networks in El Salvador 3) Cases of Application 4) Procedure for Swarm Records Purpose General Procedure Calculation of Trace Envelope Illustration of Procedure 5) Routine processing procedure 6) Availability of data 7) Future activities. Records J. Cepeda Cosmos Workshop 2
1. Introduction ti Pacific Coast in Northern Central America Subduction earthquakes (Cocos Caribbean plate boundary) Volcanic chain earthquakes 21,000 km 2 Records J. Cepeda Cosmos Workshop 3
1. Introduction ti Subduction vrs Volcanic Chain Earthquakes Differences in duration Definition of PET in instruments Long pre-event durations in Volcanic Chain Earthquakes Records J. Cepeda Cosmos Workshop 4
1. Introduction ti (cm/s 2 ) Acceleration 20 15 10 5 0-5 -10-15 -20-25 0 10 20 30 40 50 60 70 Time (s) Swarms in Volcanic Chain Earthquakes Period 1985-19991999 10 significant swarms Records of 14,000+ Earthquakes Long pre-event portions Multiple events in single record Records J. Cepeda Cosmos Workshop 5
2. Networks in El Salvador Owner institutions: Universidad Centroamericana (UCA) Servicio i Nacional de Estudios Territoriales i (SNET) Hydroelectrical Power Company (CEL) Geothermal Power Company (LAGEO) 48 digital instruments (1 instrument / 440 km 2 ) SSA-2: 25% QDR: 21% Etna: 35% K-2: 19% Records J. Cepeda Cosmos Workshop 6
2. Networks in El Salvador West (19%) Central (57%) East (24%) North (19%) Volcanic chain (69%) South (12%) Records J. Cepeda Cosmos Workshop 7
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 0 g horizontal, o ta, 0.005005 g vertical. tca Records J. Cepeda Cosmos Workshop 8
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 (M S 7.3 subduction) 1 record. 10/Oct/1986 (M S 5.4 shallow upper crustal) 6 records. 13/Jan/2001 (M S 7.8 subduction) 26 records. 13/Feb/2001 (M S 6.5 shallow upper crustal) 21 records. Largest PGA recorded: 1.1 g (13/Jan/2001, 61 km rupture distance). Records J. Cepeda Cosmos Workshop 9
3. Cases of Application Attenuation equations. Backanalysis of liquefaction phenomena. Observation of rupture directivity. Monitoring of instrumented slopes. Seismic risk scenarios. Records J. Cepeda Cosmos Workshop 10
4. Procedure for swarm records Purpose General procedure Calculation of trace envelope Illustration ti of procedure Records J. Cepeda Cosmos Workshop 11
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. Records J. Cepeda Cosmos Workshop 12
4. Procedure for swarm records General procedure 1) SSA or EVT file ASCII file. 2) Select vertical component. 3) Obtain smoothed envelope of record and amplitude of envelope. 4) Obtain crests in amplitude of envelope. 5) Obtain valleys and plains in amplitude of envelope. 6) Find values of time for lowest valleys and plains preceding crests. 7) Values of time in step (6) are cutting points. Records J. Cepeda Cosmos Workshop 13
4. Procedure for swarm records Calculation of trace envelope 1) Baseline correction (mean of record). 2) Obtain First and second derivative of record. 3) Identify flat portions (1st derivative is zero), local peaks (change of sign in 1st derivative) and identify maximum and minimum (sign of 2nd derivative). Records J. Cepeda Cosmos Workshop 14
4. Procedure for swarm records Calculation of trace envelope 4) Create vectors of maximum and minimum values. 5) Smoothing of envelope: divide record in segments of width deltat and select peaks of vectors in (4) within each segment. 6) Interpolate envelope to a fixed and uniform time step. 7) Calculate amplitude of envelope. Records J. Cepeda Cosmos Workshop 15
20 15 Record Envelope Illustration of procedure Date: 2001/May/8 Time: 18:04 Magnitude: 3.6 M L Depth: 8.2 km Epicentral distance: 9.3 km Station: HSGT (San Vicente, El Salvador) Acc celeration (cm/s 2 ) 10 5 0-5 -10-15 -20-25 0 10 20 30 40 50 60 70 Time (s) 40 Amplitude of envelope (cm/s 2 ) Slope (cm/s 3 ) 30 20 10 0-10 -20 0 10 20 30 40 50 60 70 Time (s) Records J. Cepeda Cosmos Workshop 16
5. Routine processing (SSA-2). SWS by Kinemetrics (preliminary batch processing). 1) SSA to DAT. 2) DAT to V1. 3) V1 to V2 (0.12 45 Hz). 4) V2 to V3 (-std option for calculation of SA). Records J. Cepeda Cosmos Workshop 17
5. Routine processing (SSA-2). Strong Motion Analyst by Kinemetrics (Record by record) 1) Conversion SSA to EVT format. 2) Conversion EVT to V1 unprocessed format. 3) V1 to V2 processing: a) Baseline and instrument t correction. b) High pass filtering of velocity and displacement. c) Option: Shakal and Ragsdale (1984) method. d) Corner frequencies: [0.12-0.20] Hz and 45 Hz (criteria: velocity & displacement time histories). 4) V2 to V3 (Fourier & response spectra). Records J. Cepeda Cosmos Workshop 18
6. Availability of data. www.uca.edu.sv/investigacion/terremoto/indice.htm (M S 7.8-13/Jan/2001, M S 6.5-13/Feb/2001, M W 5.1-17/Feb/2001). db.cosmos-eq.org/scripts/earthquakes.plx#cam (M S 7.8-13/Jan/2001, M S 6.5-13/Feb/2001, M W 5.1-17/Feb/2001). www.snet.gob.sv/geologia/sismologia/13%20de%20febr sv/geologia/sismologia/13%20de%20febr ero/13%20de%20febrero.htm (M S 6.5-13/Feb/2001) nsmp.wr.usgs.gov/data.usgs.gov/data_sets/ sets/20010113 0 3_ 1.html (M S 7.8-13/Jan/2001) nsmp.wr.usgs.gov/data2/cdrom_sm_1933-1986/1986/1986.zip (M S 5.4-10/Oct/1986) Records J. Cepeda Cosmos Workshop 19
7. Future activities. iti 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. Records J. Cepeda Cosmos Workshop 20
Thank you 21