How to read the reflection phases of Moho

Document Type : Research Article

Authors

1 Ph.D. Student, Institute of Geophysics, University of Tehran, Tehran, Iran

2 Assistant Professor, Seismology Department, Institute of Geophysics, University of Tehran, Tehran, Iran

3 Associate Professor, Seismology Department, Institute of Geophysics, University of Tehran, Tehran, Iran

Abstract

PmP and SmS are secondary phases that are reflected from Moho discontinuity. Moho reflected phases contain information from the entire crust, thus their travel time and waveforms contain significant information about crustal structure. We used seismogram data associated to earthquakes with magnitude larger than 3.0 and focal depth shallower than 35 km occurred during 1996-2017 in NW Iran. The seismographs of each earthquake are investigated separately. After removing mean and trend, we examined appropriate band pass filters. In this study, the response of sensor in our interest frequency (1-10HZ) is similar; thus, we did not remove instrument response.
   Particle motion of PmP reflected phase is similar to P direct phase as compressional waves and particle motion of SmS and S phases show that these phases get to stations as shear waves. If the travel time difference of picked Moho reflected and direct phases is less than 0.75 sec, picked reflected phase is reliable. We found that Butterworth band pass filter with corner frequencies of 0.5 and 4 HZ is appropriate for providing clear PmP reflected phases and the corner frequencies of 0.2 and 4 HZ are appropriate for SmS reflected phases. In general, the amplitude of the reflection phase could be shorter than the direct one due to large attenuation along the long ray path and missing some energy at the reflection boundary, but in some samples, amplitude of Moho reflected phase is larger than the direct phase, due to increment of Q values in lower crust with respect to upper crust and source of the earthquake. In this research, we often investigated the cases that amplitude of the reflection phases is larger than direct ones. We picked P and PmP from vertical component and considered the transverse and radial components for picking SmS reflected phase. S phase is read from the component where the SmS phase is more clear and noticeable. However, we can read S phase from each of the two horizontal components but in general, to avoid each time delays likely generated by anisotropy, it was read from the identical components used for picking SmS phase. Consistent with our research, the slope of the curve of difference between reflected and direct phases increases with focal depth and epicenteral distance, but for focal depth greater than Conrad discontinuity and epicenteral distance more than 80 km, the rate of increment of slope increases. Regarding this, a total of 216 PmP, 310 first P, 254 S and 161 SmS phases were picked from seismograms in the local earthquakes of NW Iran.

Keywords

Main Subjects

References

بایرام­نژاد، ا.، 1386، تعیین ساختار سرعتی پوسته در شمال غرب ایران با استفاده از وارون سازی سه بعدی داده‌های زمین لرزه­های محلی: پایان نامه دکتری، دانشگاه تهران.
جمیری، ر.، بایرام­نژاد، ا.، 1398، مکان‌یابی مجدد زمین‌لرزه­های 20 سال اخیر منطقه شمال غرب ایران با استفاده از الگوریتم JHD: مجله ژئوفیزیک ایران، 13(1)، 113-117.
فریدی، م.، سرتیبی، ا. ح.، 1391، گزارش زلزله اهر- ورزقان، سازمان زمین‌شناسی و اکتشافات معدنی کشور، مرکز تبریز.
نبوی، م. ح.، 1355، دیباچه‌ای بر زمین‌شناسی ایران: سازمان زمین‌شناسی کشور.
Ackerley, N., 2014, Principles of Broadband Seismometry: Encyclopedia of Earthquake Engineering.
Aghajany, S. H., Voosoghi, B., and Yazdian, A., 2017, Estimation of north Tabriz fault parameters using neural networks and 3D tropospherically corrected surface displacement field: Geomatics, Natural Hazards and Risk, 8(2), 918–932, https://doi.org/10.1080/19475705.2017.1289248.
Ambraseys, N. N., and Melville, C. P., 1982, A History of Persian Earthquakes: Cambridge University Press.
Aziz Zanjani, A., Ghods, A., Sobouti, F., Bergman, E., Mortezanejad, G., Priestley, K., Madanipour, M., and Rezaeian, M., 2013, Seismicity in the western coast of the South Caspian Basin and the Talesh Mountains: Geophysical Journal International, 195(2), 799–814.
Barazangi, M., Sandvol, E., and Seber, D., 2006, Structure and tectonic evolution of the Anatolian plateau in eastern Turkey, in Dilek, Y., Pavlides, S., eds., Postcollisional Tectonics and Magmatism in the Mediterranean Region and Asia: Geological Society of America.
Baruah, S., Bora, D. K., and Biswas, R., 2011, Estimation of crustal discontinuities from reflected seismic waves recorded at Shillong and Mikir Hills Plateau, Northeast India: International Journal of Earth Sciences, 100(6), 1283–1292, https://doi.org/10.1007/s00531-010-0541-2.
Berberian, M., 1977, Contribution to the Seismotectonics of Iran (part II-III): Commemoration of the 50th Anniversary of the Pahlavi dynasty, Ministry of Industry and Mines, Geological Survey of Iran, Tectonic and Seismotectonic Section, Tehran.
Berberian, M., 1997, Seismic source of the transcaucasian historical earthquakes, in Giardini, D., and Balassanian, S., eds., Historical and Prehistorical Earthquakes in Caucasus: NATO ASI Series 2, Environment-28, Kluwer Academic Press, The Netherlands, 233-311, https://doi.org/10.1007/978-94-011-5464-2_13.
Berberian, M., 2014, Patterns of historical earthquake ruptures on the Iranian plateau, in Berberian, M., ed., Developments in Earth Surface Processes: Elsevier, 439–518.
Berberian, M., and Yeats, R. S., 1999, Patterns of historical earthquake rupture in the Iranian Plateau: Bulletin of the Seismological Society of America, 89, 120–139.
Bora, D. K., Baruah, S., and Biswas, R., 2014, Moho depth variation in Shillong-Mikir Hills Plateau and its adjoining region of Northeastern India estimated from reflected and converted waves: Journal of Earthquake Science.
Cisternas, A., Philip, H., Giardini, D., and Balassanian, S., 1997, Seismotectonics of the Mediterranean region and the Caucasus, in Giardini, D., and Balassanian, S., eds., Historical and Prehistorical Earthquakes of Caucasus, 28, 39–77.
Copley, A., Faridi, M., Ghorashi, M., Hollingsworth, J., Jackson, J., Nazari, H., Oveisi, B., and Talebian, M., 2013, The 2012 August 11 Ahar earthquakes: consequences for tectonics and earthquake hazard in the Turkish–Iranian Plateau: Geophysical Journal Interantional, 196(1), 15–21.
Copley, A., and Jackson, J., 2006, Active tectonics of the Turkish-Iranian Plateau: Tectonics, 25(6), https://doi.org/10.1029/2005TC001906.
Coutant, O., 1990, Programme de simulation numérique AXITRA: Rapport LGIT-Université J. Fourier, Grenoble, Fr.
Didon, J., and Gemain, Y. M., 1976, Sabalan, Plio-Quaternary volcano of eastern Azerbaijan (Iran): geological and petrographic study of the edifice and its regional environment: Petrography, Scientific and Medical University of Grenoble.
Eftekharnejad, J., 1975, Brief history and structural development of Azerbaijan: Geological Survey of Iran: Internal Report (in Persian).
Ghods, A., Shabanian, E., Bergman, E., Faridi, M., Donner, D., Mortezanejad, G., and Aziz-Zanjani, A., 2015, The Varzaghan-Ahar, Iran, earthquake doublet (Mw 6.4, 6.2): Implications for the geodynamics of northwestern Iran: Geophysical Journal International, 203(1), 522–540, https://doi.org/10.1093/gji/ggv306.
Gupta, S., Zhao, D., Ikeda, M., and Rai, S., 2009, Crustal tomography under the Median Tectonic Line in Southwest Japan using P and PmP data: Journal of Asian Earth Sciences, 35(5), 535-542, https://doi.org/10.1016/j.jseaes.2009.01.004.
He, H., Pan, F., Chen, H., Zhang, Y., and Zheng, X., 2017, Subducting continental lower crust and crustal thickness variations in the intermediate seismic zone of Pamir-Hindu Kush inferred from Moho underside reflection PmP: Tectonophysics, 718, 132-139, https://doi.org/10.1016/j.tecto.2017.04.004.
Hessami, K., Pantosti, D., Tabassi, H., Shabanian, E., Abbassi, M. R., Feghhi, K., and Solaymani, Azad, S., 2003, Paleoearthquakes and slip rates of the North Tabriz Fault, NW Iran: Preliminary results: Annals of Geophysics, 46(5), https://doi.org/10.4401/ag-3461.
Hrubcová, P., Vavryčuk, V., Boušková, A., and Horálek, J., 2013, Moho depth determination from waveforms of microearthquakes in the West Bohemia/Vogtland swarm area: Journal of Geophysical Research: Solid Earth, 118(1), 120-137.
Jackson, J., 1992, Partitioning of strik-slip and convergent motion between Eurasia and Arabia in eastern Turkey and the Caucasus: Journal of Geophysical Research, 97, 12471–12479.
Jianshe, L., Furen, X., Congxin, L., Chengqi, X., and Shizhen, M., 2008, Seismic images under the Beijing region inferred from P and PmP data: Physics of the Earth and Planetary Interior, 168(3-4), 134–146, https://doi.org/10.1016/j.pepi.2008.06.005.
Karakhanian, A. S., Trifonov, V. G., Philip, H., et al., 2004, Active faulting and natural hazards in Armenia, eastern Turkey and northwestern
 
Iran: Tectonophysics, 380(3-4), 189–219.
Kennett, B. L. N., and Engdahl, E. R., 1991, Traveltimes for global earthquake location and phase identification: Geophysical Journal International, 105(2), 429-465, https://doi.org/10.1111/j.1365-246X.1991.tb06724.x.
Kissling, E., Kradolfer, U., and Maurer, H., 1995, VELEST user’s guide-short introduction, Technical Report: Institute of Geophysics, ETH Zürich; Switzerland.
Lechmann, A., Burg, J. P., Ulmer, P., Guillong, M., and Faridib, M., 2018, Metasomatized mantle as the source of Mid-Miocene-Quaternary volcanism in NW-Iranian Azerbaijan: Geochronological and geochemical evidence: Lithos, 304–307, 311–328, https://doi.org/10.1016/j.lithos.2018.01.030.
Lin, C. H., 2005, Identification of mantle reflections from a dense linear seismic array: Tectonic implications to the Taiwan orogeny: Geophysical Research Letters, 32(6), 1–4, https://doi.org/10.1029/2004GL021814.
Masson, F., Djamour, Y., Van Gorp, S., Chéry, J., Tatar, M., Tavakoli, F., Nankali, H., and Vernant, P., 2006, Extension in NW Iran driven by the motion of the South Caspian Basin: Earth and Planetary Science Letters, 252(1-2), 180–188, https://doi.org/10.1016/j.epsl.2006.09.038.Moradi, A. S., Hatzfeld, D., and Tatar, M., 2011, Microseismicity and seismotectonics of the North Tabriz fault (Iran): Tectonophysics, 506(1-4), 22–30, https://doi.org/https://doi.org/10.1016/j.tecto.2011.04.008.
Nakajima, J., Matsuzawa, T., and Hasegawa, A., 2002, Moho depth variation in the central part of Northeastern Japan estimated from reflected and converted waves: Physics of the Earth and Planetary Interior, 130(1-2), 31-47, https://doi.org/10.1016/S0031-9201(01)00307-7.
Priestley, K., Baker, C., and Jackson, J., 1994, Implications of earthquake focal mechanism data for the active tectonics of the South Caspian Basin and surrounding regions: Geophysical Journal International, 118(1), 111–141.
Rahimzadeh, S., Mirzaei, N., and Kaboli, M., 2021, Morphological and tectonic evidences of active faulting around and along the North Tabriz Fault zone, northwestern Iran: 39th National Conference and 4th International Congress of Earth Sciences, Tehran, Iran.
Relinger, J., and Delaitre, M., 2006, La victoire de Valmy bien vivante dans la mémoire des populations champenoise et argonnaise: Annales Histoeiques de la Revolution Française, 343, 251-253, https://doi.org/10.4000/ahrf.10402.
Salah, M. K., and Zhao, D., 2004, Mapping the crustal thickness in southwest Japan using Moho-reflected waves: Physics of the Earth and Planetary Interior, 395(1-2), 1-17, https://doi.org/10.1016/j.pepi.2003.10.002.
Shafaii Moghadam, H. S., Ghorbani, G., Zakeri Khedr, M. Z., et al., 2014, Late Miocene K-rich volcanism in the Eslamieh Peninsula (Saray), NW Iran: Implications for geodynamic evolution of the Turkish-Iranian High Plateau: Gondwana Research, 26(3-4), 1028–1050, https://doi.org/10.1016/j.gr.2013.09.015.
Lei, J., Xie, F., Lan, C., Xing, Ch., Ma, Sh., 2008, Seismic images under the Beijing region inferred from P and PmP data: Physics of the Earth and Planetary Interiors, 168(3-4), 134-146.
Sichien, E., Henriet, J. P., Camelbeeck, T., and De Baets, B., 2012, Estimating crustal thickness in Belgium and surrounding regions from Moho-reflected waves: Tectonophysics, 560–561,105–119, https://doi.org/10.1016/j.tecto.2012.06.050.
Sugan, M., and Vuan, A., 2012, Evaluating the relevance of Moho reflections in accelerometric data: Application to an inland Japanese Earthquake: Bulletin of the Seismolocical Society of America, 102(2), 842–847, https://doi.org/10.1785/0120110085.
Sun, A., Zhao, D., Ikeda, M., Yong, C., and Qifu, C., 2008, Seismic imaging of southwest Japan using P and PmP data: Implications for arc magmatism and seismotectonics: Gondwana Research, 14(3), 535-542, https://doi.org/10.1016/j.gr.2008.04.004.
Vernant, P., Nilforoushan, F., Hatzfeld, D., et al., 2004, Present-day crustal deformation and plate kinematics in the Middle East constrained by GPS measurements in Iran and northern Oman: Geophysical Journal International, 157(1), 381–398.
Xia, S. H., Qiu, X. L., Xu, H. L., Zhao, M. H., and Shi, X. B., 2011, Characteristics of PmP phases from earthquakes and their role in crustal tomography: An active volcanic area example, northeastern Japan: Science China Earth Sciences, 54(5), 640–646, https://doi.org/10.1007/s11430-010-4164-z.
Zamani, B., and Masson, F., 2014, Recent tectonics of East (Iranian) Azerbaijan from stress state reconstructions: Tectonophysics, 611, 61–82.
Zhan, Z., Ni, S., Helmberger, D. V., and Clayton, R. W., 2010, Retrieval of Moho-reflected shear wave arrivals from ambient seismic noise: Geophysical Journal International, 182(1), 408–420.
 
Iranian Journal of Geophysics
Volume 17, Issue 1
March 2023
Pages 109-128

Files

Share

How to cite

Statistics