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BACKGROUND

UNIVERSITY OF COSTA RICA ACCELEROGRAPH NETWORK: RECORDS AND APPLICATIONS By : ENG. VÍCTOR SCHMIDT MSC. Director Laboratorio de Ingeniería Sísmica. Instituto de Investigaciones en Ingeniería. Universidad de Costa Rica. BACKGROUND

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BACKGROUND

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  1. UNIVERSITY OF COSTA RICA ACCELEROGRAPH NETWORK: RECORDS AND APPLICATIONSBy: ENG. VÍCTOR SCHMIDT MSC.DirectorLaboratorio de Ingeniería Sísmica. Instituto de Investigaciones en Ingeniería. Universidad de Costa Rica

  2. BACKGROUND The Seismic Engineering Laboratory (LIS by its Spanish acronym) is the first research center exclusively dedicated to strong motion and earthquake engineering studies not only in Costa Rica but also in the whole Central American region. The LIS was born in 1989 and its consolidation was possible due to the occurrence of several important earthquakes during the beginning of the past decade. Some of those important earthquakes were: Cóbano (03/25/90, Mw = 7.0), Alajuela (12/22/90, Mw = 5.9), and Limón (04/22/91, Mw = 7.7).

  3. MAIN OBJECTIVES To develop research projects in earthquake engineering in Costa Rica. To participate in the process of revision and actualization of the “Código Sísmico de Costa Rica” (Costa Rican Seismic Code) To divulge the modern knowledge in the field of earthquake engineering among the engineering community of Costa Rica To participate in multidisciplinary research projects related to structural engineering, geotechnical engineering, seismology, urban planning, and disaster prevention.

  4. LIB Sma-Qdr TBG ETNA SRM Sma-Qdr STC Sma-Qdr TBA Sma-Qdr LIM Sma-Qdr CBN ETNA RMO ETNA RBA SSA-2 RTU SSA-2 CLD Sma-Qdr BCN Sma-Qdr CBQ ETNA ISD SSA-2 GLF ETNA RGA SSA-2 ALJ ETNA BNC SMA-1 AUR SMA-1 OVS SSA-1 INS SMA-1 RCP SMA-1 RAL ETNA Alajuela Heredia San José PCL Sma-Qdr SLG SMA-1 ETNA LPF K2 CDN SSA-1 SAB SMA-1 HTO SMA-1 ECA SSA-2 GTS Sma-Qdr FRA SSA-1 PAR SMA-1 CCH Sma-Qdr THE NETWORK Types of instruments: SMA-1 (analog): 11 SMA-QDR (Quake Digital Retrofit): 9 SSA-1 (digital): 3 SSA-2 (digital): 5 ETNA (digital): 8 K2 (digital): 1 TOTAL:37

  5. Database

  6. OBTAINING AND PROCESSING SEISMIC SIGNALS RECORDED BY THE LIS The processing of seismic signals is achieved with programs written by Kinemetrics Inc. because they are the manufacturers of the instruments that compose the network. The files obtained have a vol2 (V2) and vol3 (V3) format which allows the use of the data with other programs * VOL1DS FILE: 99A16EC1.V1 Epicentro no disponible APR 16, 1999 23:50:58.970 [k] STN 00000 0.000N 00.000W SSA S/N 0000 HYPOCENTER: 0.000N, 00.000W, H= 0.0KM. ML=0.00 INSTR PERIOD = .020 SEC DAMPING = .700 PGA_lon PGA_ver PGA_tra 9.967 5.702 12.007 NPTS= 8960 -.703E-01 -.205E+00 .101E-01 -.479E-02 -.201E+00 .993E-02 -.339E-01 -.198E+00 .974E-02 -.852E-01 -.194E+00 .955E-02 -.405E-01 -.190E+00 .936E-02 .988E-01 -.187E+00 .918E-02 .188E+00 -.183E+00 .900E-02 .130E+00 -.180E+00 .882E-02 -.436E-02 -.176E+00 .863E-02 -.799E-01 -.173E+00 .846E-02 -.594E-01 -.169E+00 .828E-02 -.127E-01 -.166E+00 .811E-02 -.922E-02 -.162E+00 .792E-02 ..... Once the filtering has been performed, the V0 files are generated. The program used to generate V0 archives from V2 was developed in the laboratory. All the output archives of this program have the same format

  7. The trigger acceleration level for analog instruments is fixed at 1%g , and 0.5%g for the digital recorders • The pre-event time for digital instruments has been assigned a value between 10s and 30s according to the distance from the station to the farthest active zone of the country. This allows that if the recorder is triggered by the arrival of s waves, complete records can be obtained if the epicenter is within 240 km away • The majority of instruments have 2g of full scale c)

  8. PROCESSING OF NOISE RECORDS AND CALCULATION OF SPECTRAL RATIOS On several occasions the laboratory has been asked to perform noise studies either to measure excessive vibrations due to machinery functioning or to determine the natural periods of soil vibration by using the Nakamura’s technique. A K2 accelerograph is used to carry out these measurements. This instrument has a full scale of 0.5g. Noise records of 1 minute with pre-event of 40s and post-event of 20s are used to apply Nakamura’s technique so that time windows of 10, 20s, etc., can be used to obtain the spectral ratios.

  9. OTHER DATA APPLICATIONS Attenuation relationships of the seismic wave Attenuation relationships for Central America and Costa Rica have been obtained by the correlation of the spectral ordinates of registered accelerograms, seismological data as magnitude and hypocentral distance and geotechnical aspects as soil type. A Bayesian type of regression analysis was used for spectral ordinates between 0.25 and 40 Hz. The general form of the used regression is: LN(I) = c1+c2*M+c3*lnr+c4*r+c5*S where I is the observed intensity parameter (acceleration or spectral velocity), M is the Moment Magnitude, r is the hypocentral distance, S is the soil type and the coefficients c1 to c2 are determined by regression

  10. Transfer functions for buildingsThe laboratory has installed analog instruments in three buildings, all of them of more than 10 floors.Considering the Hotel Aurola buillding, the accelerographs are connected; they are installed on the second basement and 15th floor. The structure of this building is made of steel and covered with concrete.

  11. Amplification of the seismic wave by soft soils, empirical methods and standard spectral ratioSome of the most important cities of Costa Rica are located on top of alluvial or ash deposits. Because of this condition, the response amplification due to the presence of soft soils is one of the most important phenomena to be evaluated in the country This method consists in locating one instrument on the ground where the measurements of the amplification are going to be made and another on an emergence of rock or hard soil. By using the similarity of the attenuation in both records as a premise, the spectral ratio between longitudinal or transversal components of both accelerograms is calculated

  12. FINAL COMMENTS AND FUTURE PLANS In order to continue with the earthquake prevention and mitigation plans is very important that the accelerograph network of the University of Costa Rica continues operating. Also, it is necessary to use processing software that allows the availability of the information in formats that can be useful for a larger quantity of researchers either national or foreign. Other objective of the laboratory is to continue investigations in the subjects mentioned above, as well as enlarging the accelerographic network, especially on the northern and southeastern regions of the country. Finally another goal is to convince the owners of high rise buildings to install digital instruments on their properties.

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