OJER  Vol.3 No.2 , May 2014
First Determination of Source Parameters of Moderate Earthquakes (4.1 ≤ M ≤ 5.1) in Morocco from Spectral Analysis
Abstract: Recent installation of an array of broad band seismological stations in Morocco allowed us to study the records of five recent (2005-2008) moderate earthquakes (4.1 ≤ M ≤ 5.1) in order to determine their source parameters (seismic moment, fault slip, rupture area and stress drop) from P-wave spectra. We also studied the older Rissani events of 1992 using teleseismic data. Values of Mo, r, Δu and Δσ are, respectively, 1.1 × 1013 - 6 × 1016 Nm; 0.50 - 3.9 km; 0.8 - 5.8 cm and 0.3 - 1.49 MPa. The results are in accordance with the seismotectonic and geodynamic setting of Morocco as, for instance, the amount of slip along the faults with respect to the relative displacement of Nubia to Iberia (~4 mm·yr-1) determined from GPS data, taking into account the period of stress accumulation. However, some events show very variable corner frequency and low-frequency amplitude values which lead to considerably higher stress drop and fault slip values, especially at the nearest stations, which may reflect some site effects or uncertainties on depth and take-off angles.
Cite this paper: Bensaid, I. , Bahi, L. and Medina, F. (2014) First Determination of Source Parameters of Moderate Earthquakes (4.1 ≤ M ≤ 5.1) in Morocco from Spectral Analysis. Open Journal of Earthquake Research, 3, 55-65. doi: 10.4236/ojer.2014.32007.

[1]   Henares, J., López Casado, C., Sanz de Galdeano, C., Delgado, J. and Peláez, J.A. (2003) Stress Fields in the Iberian-Maghrebi Region. Journal of Seismology, 7, 65-78.

[2]   Buforn, E., Bezzeghoud, M., Udias, A. and Pro, C. (2004) Seismic Sources on the Iberia-African Plate Boundary and Their Tectonic Implications. Pure and Applied Geophysics, 161, 623-646.

[3]   Medina, F. and El Alami, S.O. (2006) Focal Mechanisms and State of Stress in the Al Hoceima Area (Central Rif, Morocco). Bulletin de l’Institut Scientifique, Section Sciences de la Terre, 28, 19-30.

[4]   Stich, D., Serpelloni, E., Mancilla, F. and Morales, J. (2006) Kinematics of the Iberia-Maghreb Plate Contact from Seismic Moment Tensors and GPS Observations. Tectonophysics, 426, 295-317.

[5]   Serpelloni, E., Vannucci, G., Pondrelli, S., Argnani, A., Casula, G., Anzidei, M., Baldi, P. and Gasperini, P. (2007) Kinematics of the Western Africa-Eurasia Plate Boundary from Focal Mechanisms and GPS Data. Geophysical Journal International, 169, 1180-1200.

[6]   de Vicente, G., Cloetingh, S., Muñoz-Martin, A., Olaiz, A., Stich, D., Vegas, R., Galindo-Zaldivar, J. and Fernandez-Lozano, J. (2008) Inversion of Moment Tensor Focal Mechanisms for Active Stresses around the Microcontinent Iberia: Tectonic Implications. Tectonics, 27, TC1009.

[7]   DeMets, C., Gordon, R.G. and Argus, D.F. (2010) Geologically Current Plate Motions. Geophysical Journal International, 181, 1-80.

[8]   Vernant, P., Fadil, A., Mourabit, T., Ouazar, D., Koulali, A., Davila, J.M., Garate, J., McClusky, S. and Reilinger, R. (2010) Geodetic Constraints on Active Tectonics of the Western Mediterranean: Implications for the Kinematics and Dynamics of the Nubia-Eurasia Plate Boundary Zone. Journal of Geodynamics, 49, 123-129.

[9]   Pedrera, A., Ruiz-Constán, A., Galindo-Zaldívar, J., Chalouan, A., Sanz de Galdeano, C., Marín-Lechado, C., Ruano, P., Benmakhlouf, M., Akil, M., López-Garrido, A.C., Chabli, A., Ahmamou, M. and González-Castillo, L. (2011) Is There an Active Subduction Beneath the Gibraltar Orogenic Arc? Constraints from Pliocene to Present-Day Stress Field. Journal of Geodynamics, 52, 83-96.

[10]   Bensaid, I., Buforn, E., Cherkaoui, T.-E., Medina, F. and Hahou, Y. (2011) New Fault-Plane Solutions of Moroccan Earthquakes for the 2005-2008 Period. Bulletin de l’Institut Scientifique, Section Sciences de la Terre, 33, 47-52.

[11]   Nocquet, J.-M. (2012) Present-Day Kinematics of the Mediterranean: A Comprehensive Overview of GPS Results. Tectonophysics, 579, 220-242.

[12]   Fadil, A., Vernant, P., McClusky, S., Reilinger, R., Gomez, F., Ben Sari, D., Mourabit, T., Feigl, K. and Barazangi, M. (2006) Active Tectonics of the western Mediterranean: Geodetic Evidence for Rollback of a Delaminated Subcontinental Lithospheric Slab Beneath the Rif Mountains, Morocco. Geology, 34, 529-532.

[13]   Tahayt, A., Mourabit, T., Rigo, A., Feigl, K.L., Fadil, A., McClusky, S., Reilinger, R., Serroukh, M., Ouazzani- Touhami, A., Ben Sari, D. and Vernant, P. (2008) Mouvements actuels des blocs tectoniques dans l’arc Bético-Rifain à partir des mesures GPS entre 1999 et 2005. C. R. Geoscience, 340, 400-413.

[14]   Chalouan, A., Gil, A.J., Galindo-Zaldívar, J., Ahmamou, M., Ruano, P., de Lacy, M.C., Ruiz-Armenteros, A.M., Benmakhlouf, M. and Riguzzi, F. (2014) Active Faulting in the Frontal Rif Cordillera (Fes Region, Morocco): Constraints from GPS Data. Journal of Geodynamics, in press.

[15]   Chalouan, A., Galindo-Zaldívar, J., Akil, M., Marín, C., Chabli, A., Ruano, P., Bargach, K., Sanz de Galdeano, C., Benmakhlouf, M., Ahmamou, M. and Gourari, L. (2006) Tectonic Wedge Escape in the Southwestern Front of the Rif Cordillera (Morocco). In: Moratti, G. and Chalouan, A., Eds., Tectonics of the Western Mediterranean and North Africa, Geological Society, London, Special Publication 262, 101-118.

[16]   Ben Sari, D. (1978) Connaissance géophysique du Maroc. State Thesis, University Joseph Fourier, Grenoble.

[17]   Hatzfeld, D. (1978) Etude sismotectonique de la zone de collision Ibéro-Maghrébine. State Thesis, University Joseph Fourier, Grenoble.

[18]   Frogneux, M. (1980) La sismicité marocaine de 1972 à 1978. Etude des paramètres à la source des séismes proches. Troisième Cycle Thesis, University of Grenoble, Grenoble.

[19]   Cherkaoui, T.E. (1988) Fichier des séismes du Maroc et des régions voisines 1901-1984. Travaux de l’Institut Scientifique, Série Géologie et Géographie physique, 17, 1-168.

[20]   Cherkaoui, T.E. (1991) Contribution à l'étude de l'aléa sismique au Maroc. Thesis, University of Grenoble, Grenoble.

[21]   Bezzeghoud, M. and Buforn, E. (1999) Source Parameters of the 1992 Melilla (Spain, Mw = 4.8), 1994 Alhoceima (Morocco, Mw = 5.8) and 1994 Mascara (Algeria, Mw = 5.7) Earthquakes and Seismotectonic Implications. Bulletin of the Seismological Society of America, 89, 359-372.

[22]   El Alami, S.O., Tadili, B., Brahim, L.A. and Mouayn, I. (2004) Seismicity of Morocco for the Period 1987-1994. Pure and Applied Geophysics, 161, 969-982.

[23]   Hatzfeld, D. and Frogneux, M. (1981) Intermediate Depth Seismicity in the Western Mediterranean Unrelated to Subduction of Oceanic Lithosphere. Nature, 292, 443-445.

[24]   Medina, F. (2008) Catalogue of Focal Mechanisms of the Moroccan Earthquakes for the Period 1959-2007. Documents de l’Institut Scientifique, Rabat, No. 22, 1-56.

[25]   Jabour, N. (1993) Source Process of Earthquakes in the Atlantic Ocean and Morocco. International Institute of Earthquake Engineering, Individual Studies, Course 1992-1993, No. 29, 1-13.

[26]   Bensaid, I., Cherkaoui, T.E., Medina, F., Caldeira, B., Buforn, E., Emran, A. and Hahou, Y. (2012) The 1992 Tafilalt Seismic Crisis (Anti-Atlas, Morocco). Journal of Seismology, 16, 35-53.

[27]   Díaz, J., Villaseñor, A., Gallart, J., Morales, J., Pazos, A., Córdoba, D., Pulgar, J., García-Lobón, J.L., Harnafi, M. and TopoIberia Seismic Working Group (2008) The IBERARRAY Broadband Seismic Network: A New Tool to Investigate the Deep Structure Beneath Iberia. ORFEUS Newsletter, 8, 1-6.

[28]   Pazos, A., Davila, J.M., Buforn, E., Pasquín, J., Morollón, M.C., Hanka, W., Udías, A., Bezzeghoud, M., Harnafi, M. and the ROA Seismic Team (2010) Multi-Parameter Observations in the Ibero-Moghrebian Region: The Western Me- diterranean Seismic Network (WM) and ROA GPS Geodynamic Network. EGU General Assembly 2010, 2-7 May 2010, Vienna, 9865.

[29]   Kiratzi, A. and Louvari, E. (2001) Source Parameters of the Izmit-Bolu 1999 (Turkey) Earthquake Sequences from Te- leseismic Data. Annals of Geophysics, 44, 33-47.

[30]   Benetatos, C., Roumelioti, Z., Kiratzi, A. and Melis, N. (2001) Source Parameters of the M 6.5 Skyros Island (North Aegean Sea) Earthquake of July 26, 2001. Annals of Geophysics, 45, 513-526.

[31]   Stavrakakis, G.N., Chouliaras, G. and Panoupoulou, G. (2002) Seismic Source Parameters for the ML = 5.4 Athens Earthquake (7 September 1999) from a New Telemetric Broad Band Seismological Network in Greece. Natural Ha- zards, 27, 47-60.

[32]   Lee, W.H.K. and Valdés, C.M. (1985) HYPO71PC: A Personal Computer Version of the HYPO71 Earthquake Loca- tion Program. U.S. Geological Survey, Open-File Report, 85-749.

[33]   Brillinger, D.R., Udias, A. and Bolt, B.A. (1980) A Probability Model for Regional Focal Mechanism Solutions. Bu- lletin of the Seismological Society of America, 70, 149-170.

[34]   Brune, J.N. (1970) Tectonic Stress and the Spectra of Seismic Shear Waves from Earthquakes. Journal of Geophysical Research, 75, 4997-5009.

[35]   Brune, J.N. (1971) Correction [to “Tectonic Stress and the Spectra of Seismic Shear Waves from Earthquakes”]. Journal of Geophysical Research, 76, 5002.

[36]   Kanamori, H. and Anderson, D.L. (1975) Theoretical Basis of Some Empirical Relations in Seismology. Bulletin of the Seismological Society of America, 65, 1073-1095.

[37]   Keilis-Borok, V.I. (1960) Investigation of the Mechanism of Earthquakes. Soviet Research in Geophysics (English translation), 4, 29.

[38]   Udias, A. (1999) Principles of Seismology. Cambridge University Press, Cambridge.

[39]   Eshelby, J.D. (1957) The Determination of the Elastic Field of an Ellipsoidal Inclusion, and Related Problems. Pro- ceedings of the Royal Society of London. Series A, 241, 376-396.

[40]   Goldstein, P. and Snoke, A. (2005) SAC Availability for the IRIS Community. Incorporated Research Institutions for Seismology Newsletter.

[41]   Kane, D.L., Prieto, G.A., Vernon, F.L. and Shearer, P.M. (2011) Quantifying Seismic Source Parameter Uncertainties. Bulletin of the Seismological Society of America, 101, 535-543.