Rapidly Estimated Seismic Source Parameters for the 16 September 2015 Illapel, Chile M w 8.3 Earthquake
- 849 Downloads
On 16 September 2015, a great (M w 8.3) interplate thrust earthquake ruptured offshore Illapel, Chile, producing a 4.7-m local tsunami. The last major rupture in the region was a 1943 M S 7.9 event. Seismic methods for rapidly characterizing the source process, of value for tsunami warning, were applied. The source moment tensor could be obtained robustly by W-phase inversion both within minutes (Chilean researchers had a good solution using regional data within 5 min) and within an hour using broadband seismic data. Short-period teleseismic P wave back-projections indicate northward rupture expansion from the hypocenter at a modest rupture expansion velocity of 1.5–2.0 km/s. Finite-fault inversions of teleseismic P and SH waves using that range of rupture velocities and a range of dips from 16°, consistent with the local slab geometry and some moment tensor solutions, to 22°, consistent with long-period moment tensor inversions, indicate a 180- to 240-km bilateral along-strike rupture zone with larger slip northwest to north of the epicenter (with peak slip of 7–10 m). Using a shallower fault model dip shifts slip seaward toward the trench, while a steeper dip moves it closer to the coastline. Slip separates into two patches as assumed rupture velocity increases. In all cases, localized ~5 m slip extends down-dip below the coast north of the epicenter. The seismic moment estimates for the range of faulting parameters considered vary from 3.7 × 1021 Nm (dip 16°) to 2.7 × 1021 Nm (dip 22°), the static stress drop estimates range from 2.6 to 3.5 MPa, and the radiated seismic energy, up to 1 Hz, is about 2.2–3.15 × 1016 J.
Keywords2015 Illapel earthquake Chilean seismic gaps rupture process seismic rupture parameters
We thank Luis Rivera for his program for calculating stress drop for variable slip models, and Charles Ammon for sharing preliminary R1 source time functions and their azimuthal patterns. Sebastian Riquelme provided information on the regional W-phase inversion that helped guide the tsunami alert and evacuation. The IRIS DMS data center was used to access the seismic data from Global Seismic Network and Federation of Digital Seismic Network stations. We thank the editor and two anonymous reviewers for helpful comments on the manuscript. This work was supported by NSF grant EAR1245717 (T. L.).
- Abe, K. (1981), Magnitudes of large shallow earthquakes from 1904 to 1980, Phys. Earth Planet. Intr., 27, 72–92.Google Scholar
- Beck, S., S. Barrientos, E. Kausel, and M. Reyes (1998), Source characteristics of historic earthquakes along the central Chile subduction zone, J. South American Earth Sci., 11, 115–129.Google Scholar
- Brodsky, E. E., and T. Lay (2014), Recognizing foreshocks from the 1 April 2014 Chile earthquake, Science, 344, 700–702.Google Scholar
- Brooks, B. A., M. Bevis, R. Smalley Jr., E. Kendrick, R. Manceda, E. Lauría, R. Maturana, and M. Araujo (2003), Crustal motion in the Southern Andes (26°–36°S): Do the Andes behave like a microplate? Geochem., Geophys., Geosys., 4(10), 1085. doi: 10.1029/2003GC000505.
- Christensen, D. H., and L. J. Ruff (1986), Rupture process of the March 3, 1985 Chilean earthquake, Geophys. Res. Lett., 13, 721–724.Google Scholar
- Comte, D., A. Eisenberg, E. Lorca, M. Pardo, L. Ponce, R. Saragoni, S. K. Singh, and G. Suárez (1986), The 1985 central Chile earthquake: a repeat of previous great earthquakes in the region? Science, 233(4762), 449–453.Google Scholar
- Convers, J. A., and A. V. Newman (2011), Global evaluation of large earthquake energy from 1997 through mid-2010, J. Geophys. Res., 116, B08304, doi: 10.1029/2010JB007928.
- DeMets, C., Gordon, R. G., Argus, D. F. (2010), Geologically current plate motions, Geophys. J. Int., 181, 1–80. doi: 10.1111/j.1365-246X.2009.04491.x.
- Duputel, Z., L. Rivera, H. Kanamori, and G. Hayes (2012), W phase source inversion for moderate to large earthquakes (1990–2010), Geophys. J. Int., 189, 1125–1147, doi: 10.1111/j.1365-246X.2012.05419.x.
- Duputel, Z., V. C. Tsai, L. Rivera, and H. Kanamori (2013), Using centroid time-delays to characterize source durations and identify earthquakes with unique characteristics, Earth Planet Sci. Lett., 375, 92–100, doi: 10.1016/j.epsl.2013.05.024.
- Gardi, A., A. Lemoine, R. Madariaga, and J. Campos (2006), Modeling of stress transfer in the Coquimbo region of central Chile, J. Geophys. Res., 111, B04307, doi: 10.1029/2004JB003440.
- Hartzell, S. H., and T. H. Heaton (1983), Inversion of strong ground motion and teleseismic waveform data for the fault rupture history of the 1979 Imperial Valley, California, earthquake, Bull. Seismol. Soc. Am., 73(6A), 1553–1583.Google Scholar
- Hayes, G.P., and D. J. Wald (2009), Developing framework to constrain the geometry of the seismic rupture plane in subduction zones a priori—a probabilistic approach, Geophys. J. Int. 176, 951–964, 2009.Google Scholar
- Hayes, G. P., D. J. Wald, and R. L. Johnson (2012), Slab1.0: A three-dimensional model of global subduction zone geometries, J. Geophys. Res., 117, B01302, doi: 10.1029/2011JB008524.
- Holtkamp, S. G., M. E. Pritchard, and R. B. Lohman (2011), Earthquake swarms in South America, Geophys. J. Int., 187, 128–146, doi: 10.1111/j.1365-246X.2011.05137.x.
- Kanamori, H., and L. Rivera (2008), Source inversion of W phase: speeding up seismic tsunami warning, Geophys. J. Int., 175, 222–238, doi: 10.1111/j.1365-246X.2008.03887.x.
- Kelleher, J.A. (1972), Rupture zones of large South American earthquakes and some predictions. J. Geophys. Res., 77(11), 2087–2103.Google Scholar
- Kendrick, E., M. Bevis, R. Smalley, O. Cifuentes, and F. Galban (1999), Current rates of convergence across the Central Andes: Estimates from continuous GPS observations, Geophys. Res. Lett., 26, 541–544.Google Scholar
- Kendrick, E., M. Bevis, R. Smalley Jr., and B. Brooks (2001), An integrated crustal velocity field for the central Andes, Geochem. Geophys. Geosys., 2, doi: 10.1029/2001GC000191.
- Khazaradze, G., and J. Klotz (2003), Short and long-term effects of GPS measured crustal deformation rates along the South-Central Andes, J. Geophys. Res., 108, B4, 1–13, doi: 10.1029/2002JB001879.
- Kikuchi, M., H. Kanamori (1991), Inversion of complex body waves—III. Bull. Seismol. Soc. Am., 81(6), 2335–2350.Google Scholar
- Laske, G., G. Masters., Z. Ma, and M. Pasyanos (2013), Update on CRUST1.0—A 1-degree Global Model of Earth’s Crust, Geophys. Res. Abstracts, 15, Abstract EGU2013-2658, 2013.Google Scholar
- Lay, T., H. Kanamori, C. J. Ammon, K. D. Koper, A. R. Hutko, L. Ye, H. Yue, and T. M. Rushing (2012), Depth-varying rupture properties of subduction zone megathrust faults, J. Geophys. Res., 117, B04311, doi: 10.1029/2011JB009133.
- Lay, T., Yue, H., E. E. Brodsky, and C. An (2014), The 1 April 2014 Iquique, Chile Mw 8.1 earthquake rupture sequence, Geophys. Res. Lett., 41, doi: 10.1002/2014GL060238.
- Lomnitz, C. (1971). Grandes terremotos y tsunamis en Chile durante el period 1535–1955, Geofisica Panamericana, 1(1), 151–178.Google Scholar
- Métois, M., A. Socquet, and C. Vigny (2012), Interseismic coupling, segmentation and mechanical behavior of the central Chile subduction zone, J. Geophys. Res., 117, B03406, doi: 10.1029/2011JB008736.
- Moreno, M., M. Rosenau, and O. Oncken (2010), 2010 Maule earthquake slip correlates with pre-seismic locking of Andean subduction zone, Nature, 467, 198–202, doi: 10.1038/nature09349.
- Nishenko, S. P. (1985), Seismic potential for large and great interplate earthquakes along the Chilean and southern Peruvian margins of South America: a quantitative reappraisal, J. Geophys. Res., 90, 3589–3615.Google Scholar
- Noda, H., N. Lapusta, and H. Kanamori (2013), Comparison of average stress drop measures for ruptures with heterogeneous stress change and implications for earthquake physics, Geophys. J. Int., 193, 1691–1712, doi: 10.1093/gji/ggt074.
- Norabuena, E., L. Leffler-Griffin, A. Mao, T. Dixon, S. Stein, S. I. Sacks, L. Ocola, and M. Ellis (1998), Space geodetic observations of Nazca–South America convergence across the central Andes, Science, 270, 358–362.Google Scholar
- Storchak, D.A., D. Di Giacomo, I. Bondár, E. R. Engdahl, J. Harris, W. H. K. Lee, A. Villaseñor, and P. Bormann (2013). Public release of the ISC-GEM global instrumental earthquake catalogue (1900–2009), Seism. Res. Lett., 84(5), 810–815, doi: 10.1785/0220130034.
- Venkataraman, A., and H. Kanamori (2004), Observational constraints on the fracture energy of subduction zone earthquakes, J. Geophys. Res., 109, B05302, doi: 10.1029/2003JB002549.
- Vigny, C., A. Rudloff, J.-C. Ruegg, R. Madariaga, J. Campos, and M. Alvarez (2009), Upper plate deformation measured by GPS in the Coquimbo gap, Chile, Phys. Earth Planet. Inter., 175(1–2), 86–95.Google Scholar
- X u, Y., K. D. Koper, O. Sufri, L. Zhu, A. R. Hutko (2009), Rupture imaging of the M W 7.9 12 May 2008 Wenchuan earthquake from back projection of teleseismic P waves, Geochem. Geophys. Geosyst., 10, Q04006, doi: 10.1029/2008GC002335.
- Ye, L., T. Lay, H. Kanamori, and K. D. Koper (2013a), Energy release of the 2013 M W 8.3 Sea of Okhotsk earthquake and deep slab stress heterogeneity, Science, 341, 1380–1383, doi: 10.1126/science.1242032.
- Ye, L., T. Lay, and H. Kanamori (2013b), Large earthquake rupture process variations on the Middle America megathrust, Earth Planet. Sci. Lett., 381, 147–155, doi: 10.1016/j.epsl.2013.08.042.
- Yue, H., T. Lay, L. Rivera, C. An, C. Vigny, X. Tong, and J. C. Báez Soto (2014), Localized fault slip to the trench in the 2010 Maule, Chile M w 8.8 earthquake from joint inversion of high-rate GPS, teleseismic body waves, InSAR, campaign GPS, and tsunami observations, J. Geophys. Res., 119, 7786–7804, doi: 10.1002/2014JB011340.