بانک داده‌های منتخب حرکات قوی زمین برای زلزله‌های ایران

نوع مقاله : Articles

نویسندگان

1 پژوهشکده زلزله شناسی، پژوهشگاه بین المللی زلزله شناسی و مهندسی زلزله، تهران

2 پژوهشگاه بین المللی زلزله شناسی و مهندسی زلزله، تهران

چکیده

جمع­آوری اطلاعات مربوط به داده‌های ثبت‌شده بر اثر زمین­لرزه و تجزیه‌وتحلیل آنها می‌تواند جهت مطالعات تحلیل خطر، ریسک و یا رویکردهای مهندسی زلزله مفید واقع شود. در این مقاله، گزارشی از روند تهیه یک بانک داده‌ی منتخب از رکوردهای حرکات قوی زمین در ایران ارائه شده است. از مجموع بیش از 10000 رکورد سه‌مؤلفه‌ای که تماماً از رکوردهای ثبت­شده توسط شبکه‌ی شتاب‌نگاری کشوری مرکز تحقیقات راه، مسکن و شهرسازی در بین سال­های 1976 تا 2015 برداشت شده ­است، 2286 رکورد مناسب و دارای کیفیت قابل­قبول انتخاب گردیدند. این رکوردها حاصل از 461 رویداد زلزله می‌باشد که بزرگای گشتاوری آنها در محدوده‌ی 9/3 تا 3/7 قرار دارد و از هر زلزله حداقل دو رکورد در بانک داده‌های معرفی‌شده موجود می‌باشد. برای نخستین بار، فاصله‌ی ایستگاه ثبت­کننده‌ی تصویر افقی سطح گسل در روی سطح زمین برای تعداد زیادی رکورد که بزرگای زلزله‌ی مربوطه عمدتاً بیش از 6 بوده است، در این بانک داده با دقت زیاد گزارش شده است. شایان‌ذکر است که شتاب‌نگاشت‌های ثبت­شده که به‌صورت خام در دسترس بوده‌اند با استفاده از روش پردازش مبتنی بر الگوریتم موجک نوفه­زدایی شده‌اند. پارامترهای مختلفی همچون بیشینه شتاب، شتاب طیفی در دوره تناوب‌های مختلف (تا دوره تناوب 4 ثانیه)، مدت‌زمان مؤثر، مدت‌زمان دوام برای هر سه مؤلفه‌ی رکورد ثبت‌شده محاسبه شده است. همچنین نوع خاک در ایستگاه ثبت­کننده‌ی رکورد و نوع گسلش زلزله نیز گزارش شده است. همچنین یک بازبینی برای مشخصات زلزله شامل موقعیت مرکز زلزله، بزرگا، نوع گسلش و همچنین هندسه‌ی صفحه‌ی گسیختگی گسل (در صورت امکان) صورت پذیرفته است. در نهایت برخی از رکوردهایی که دارای بیشینه شتاب بیش از 3 متر بر مجذور ثانیه و ثبت‌شده در فاصله‌ای کمتر از 30 کیلومتر بوده‌اند، به‌عنوان رکوردهای خاص معرفی شده‌اند.

کلیدواژه‌ها


عنوان مقاله [English]

A Database of the Iranian Strong Motion Records

نویسندگان [English]

  • Hamid Zafarani 1
  • Mohammad Reza Soghrat 2
1 International Institute of Earthquake Engineering and Seismology (IIEES), Iran
2 International Institute of Earthquake Engineering and Seismology (IIEES), Iran
چکیده [English]

The Iranian plateau, located along the Alpine–Himalayan orogenic belt, is one of the tectonically active regions of shallow crustal earthquakes. Therefore, development of a strong ground-motion dataset with appropriate quality and content is an essential component/tool in local ground-motion studies and for engineering practice.
The first strong-motion instruments were installed in 1973. Since then, the number of strong-motion stations has been gradually increased. Currently, the Iranian strong-motion dataset includes more than 10000 three-component time series, which are recorded at about 1100 permanent stations.
By probing into the quality of the records and the metadata information, 2286 time series recorded on 743 stations from 461 earthquakes with a maximum moment magnitude of 7.3 are chosen. The moment magnitudes have been provided from international or local seismological agencies or from earthquake-specific literature studies in about 40 % of events. For the remaining events, the empirical magnitude conversion equations are used to obtain the more homogenous magnitude information and increase the number of events associated with moment magnitude values. The calculated moment magnitudes are mainly less than 5. The converted moment magnitudes belong to small earthquakes that are originally reported with magnitude scales of Nuttli (MN), Local (ML), body-wave (mb) and surface-wave (Ms).
The bulk of events in the dataset are shallow continental earthquakes with depths less than 30 km. About 75%    of events are in this range of the mentioned focal depth. The number of earthquakes with unknown focal depth is less than 1% in the selected dataset. The events of depths ranging more than 40 km are mainly from the Zagros region. For about 66% of events, there is no information available‌ (NA) about their faulting mechanisms. The dominant faulting mechanisms are reverse (20% of events) and strike-slip faulting (12% of events). A minority of events and accelerograms are related to the normal faulting mechanism. 
Most of the unknown faulting mechanisms are attributed to events with small magnitude (Mw ≤ 5) due to the lack of double-couple fault-plane solutions for these earthquakes. Large events have been studied to determine the faulting mechanisms due to their importance while on the small events are rarely focused.
About 743 stations have provided accelerometric data in the selected dataset. The average shear-wave velocity between 0 m and 30 m depth (Vs30) in more than 40% of these stations have been measured and reported by the BHRC. The site classes for about 299 stations have been proposed either by geological surveys or by empirical methods (using H/V method). Therefore, we have no information about the soil categories for only 138 stations because they are either temporary stations or stations that recorded accelerograms less than 5 times. Considering    the Vs30 criteria, the majority of the stations are belonged to site class II while the most of the stations will be in site class III if we use only the above-mentioned empirical method.
During the data processing, the records with the following features have been eliminated from the dataset: data from instruments that triggered during the S-wave train; the records with only a single horizontal component; and the records obtained from events with unknown or poor estimates of magnitude (which are attributed to the small
events). Furthermore, the records with non-standard error such as very high-frequency spikes, multi-event, and so on are excluded from the dataset.
The aim of this paper is first to present the new catalog with comprehensive metadata for engineering and research practices. The record selection for development of new GMPEs for various strong-motion parameters can be performed by using the provided catalog. In addition, the main features of the Iranian strong-motion dataset have been provided in this paper. To this end, a careful revision of the characteristics of the earthquakes such as location, magnitude, style of faulting and fault rupture plane geometry, if available, has been scientifically performed for the first time using the best available information. Finally, we concentrate on special ground-motion records including records with peak ground acceleration PGA > 300 cm/s/s and distances less than 30 km. These are designated as “distinct” records in the Iranian dataset because they include less than 2% of the selected dataset.

کلیدواژه‌ها [English]

  • Strong Motion
  • database
  • Records
  • Iran
  1. Kale, Ö., Akkar, S., Ansari, A., and Hamzehloo, H. (2015) A Ground-Motion Predictive Model for Iran and Turkey for Horizontal PGA, PGV, and 5% Damped Response Spectrum: Investigation of Possible Regional Effects. Bulletin of the Seismological Society of America, 105, 963-980.
  2. Saffari, H., Kuwata, Y., Takada, S., and Mahdavian, A. (2012) Updated PGA, PGV, and spectral acceleration attenuation relations for Iran. Earthquake Spectra, 28, 257-276.
  3. Mirzaei, N., Mengtan, G., and Yuntai, C. (1998) Seismic source regionalization for seismic zoning of Iran: major seismotectonic provinces. J. Earthq. Pred. Res., 7, 465-495.
  4. Engdahl, E.R., Jackson, J.A., Myers, S.C., Bergman, E.A., and Priestley, K. (2006) Relocation and assessment of seismicity in the Iran region. Geophys. J. Int., 167, 761-78.
  5. Shahvar, M.P., Zare, M., Castellaro, S. (2013) A Unified Seismic Catalog for the Iranian Plateau (1900–2011). Seismo. Res. Let., 84, 233-249.
  6. Zafarani, H. and Hassani, B. (2013) Site response and source spectra of S-waves in the Zagros region. Iran J. Seismol., 17, 645-666.
  7. Zafarani, H., Hassani, B., and Ansari, A. (2012) Estimation of earthquake parameters in the Alborz seismic zone, Iran using generalized inversion method. Soil Dyn. Earthq. Eng., 42, 197-218.
  8. Zafarani, H., Rahimi, M., Noorzad, A., Hassani, B., Khazaei, B. (2015) Stochastic simulation of strong‐motion records from the 2012 Ahar–Varzaghan Dual Earthquakes, Northwest of Iran. Bulletin of the Seismological Society of America, 105(3), 1419-1434.
  9. Ghasemi, H., Zare, M., Fukushima, Y., and Sinaeian, F. (2009b) Applying empirical methods in site classification, using response spectral ratio (H/V): A case study on Iranian strong motion network (ISMN). Soil Dyn. Earthq. Eng., 29, 121-132.
  10. Boore, D.M. and Bommer, J.J. (2005) Processing of strong-motion accelerograms: needs, options and consequences. Soil Dyn. Earthq. Eng., 25, 93-115.
  11. Boore, D.M., Stephens, C.D., and Joyner, W.B. (2002) Comments on baseline correction of digital strong-motion data: examples from the 1999 Hector Mine, California earthquake. Bulletin of the Seismological Society of America, 92, 1543-1560.
  12. Boore, D.M. (2003) Analog-to-digital conversion as a source of drifts in displacements derived from digital recordings of ground acceleration. Bulletin of the Seismological Society of America, 93, 2017-2024.
  13. Akkar, S., Çağnan, Z., Yenier, E., Erdoğan, Ö., Sandıkkaya, M.A., and Gülkan, P. (2010) The recently compiled Turkish strong motion database: preliminary investigation for seismological parameters. Journal of Seismology, 14, 457-479
  14. Kamai, R., Abrahamson, N., and Graves, R. (2014) Adding fling effects to processed ground-motion time histories. Bulletin of the Seismological Society of America, 104.
  15. Boore, D.M. and Akkar, S. (2003) Effect of causal and acausal filters on elastic and inelastic response spectra. Earthquake Eng. Struct. Dyn., 32, 1729-1748.
  16. Ansari, A., Noorzad, A., Zafarani, H., and Vahidifard, H. (2010) Correction of highly noisy strong motion records using a modified wavelet denoising method. Soil Dyn. Earthq. Eng., 30, 1168-1181.
  17. Boore, D.M. and Thompson, E.M. (2014) Path durations for use in the stochastic-method simulation of ground motions. Bulletin of the Seismological Society of America, 104, 2541-2552.
  18. Bommer, J.J., Stafford, P.J., and Alarcon, J.E. (2009) Empirical equations for the prediction of the significant, bracketed, and uniform duration of earthquake ground motion. Bulletin of the Seismological Society of America, 99(6), 3217-3233.
  19. Hassani, B., Zafarani, H., Farjoodi, J., and Ansari, A. (2011) Estimation of site amplification, attenuation and source spectra of S-waves in the East-Central Iran. Soil Dynamics and Earthquake Engineering, 31(10), 1397-1413.