Rupture evolution of the 2006 Java tsunami earthquake and the possible role of splay faults
Introduction
Tsunami earthquakes are characterized by a disproportionately large tsunami for their size, and often exhibit a disparity between estimates of moment magnitude derived from long and short period seismic radiation Kanamori, 1972, Kanamori and Kikuchi, 1993. The July 17, 2006 Java earthquake was a classic tsunami earthquake with body-wave magnitude mb = 6.1, surface-wave magnitude Ms = 7.1, and moment magnitude Mw = 7.7 Ekström et al., 2012, International Seismological Centre, 2013. Such a large variation in magnitude estimates is atypical and may indicate a deficiency in high-frequency radiation compared to low-frequency radiation Ammon et al., 2006, Newman and Okal, 1998. The 2006 Java earthquake initiated at shallow depth (20 km, (International Seismological Centre, 2013); Fig. 1) and ruptured eastward along the trench axis for ∼200 km Ammon et al., 2006, Bilek and Engdahl, 2007. Given the source dimension, the unusually long source duration (∼185 s) indicates anomalously slow rupture propagation for the event Ammon et al., 2006, Bilek and Engdahl, 2007. The earthquake generated a large tsunami (∼8 m) resulting in over 800 fatalities Fritz et al., 2007, Fujii and Satake, 2006, Mori et al., 2007. This was the second tsunami earthquake that struck the Java region since instrumental records began, and a Mw 7.8 earthquake in June 1994 produced an even larger tsunami (∼13 m), resulting in 250 fatalities Abercrombie et al., 2001, Mori et al., 2007. These two earthquakes are only 600 km apart, highlighting the major tsunami hazard along the south coast of Indonesia (Mori et al., 2007). Is the Java trench prone to more tsunami earthquakes and if so, what properties of the margin promote this type of rupture?
Finite-fault slip models of the 2006 Java earthquake suggest a smooth slip distribution with an unusually slow (∼1 km/s) rupture propagation (Fig. 2b). Finite-fault slip models obtained from body waves (P and SH waves, ∼0.001–0.2 Hz) have similar slip distributions, with the largest slip concentrated near the hypocenter (Fig. 2b) Ammon et al., 2006, Bilek and Engdahl, 2007, Yagi and Fukahata, 2011, Ye et al., 2016, Ye et al., 2016. In contrast, finite-fault slip models obtained from both body and surface waves (both Rayleigh and Love waves) suggest that the largest slip is close to the trench and is up-dip and ∼50 km east of the hypocenter (Fig. 2) Hayes, 2011, Shao et al., 2011. Surface waves have been shown to be effective at resolving near-trench slip distributions, which are difficult to resolve just with body waves (Shao et al., 2011).
The 2006 Java earthquake was one of the best-recorded tsunami earthquakes with modern instruments. Combining the wealth of data with new observational approaches enables us to investigate the earthquake in great detail. We first analyze bathymetry and gravity anomalies in conjunction with active-source seismic profiles to constrain margin structure and the location of splay faults. We then build on published kinematic slip models of the 2006 Java earthquake source by performing global P-wave back-projection using two different frequency bands to examine the earthquake kinematics. In addition, we back-propagate first-crest arrivals in tsunami waveforms of five nearby tide gauges at various azimuths to locate tsunami sources. Our high-frequency back-projection results suggest a unilateral rupture extending ∼200 km with a slow first-stage rupture (∼1.2 km/s) from west to east until ∼65 s and a fast second-stage rupture (∼ 2.7 km/s) from ∼65 to 150 s. The second-stage rupture colocates with a major tsunami source located by first-crest tsunami back-propagation. The spatial correlation between the stage-two rupture imaged by back-projection and splay fault traces delineated by gravity data suggests that splay faults may have been reactivated during the 2006 Java earthquake and possibly contributed to tsunamigenesis. This mechanism of enhanced tsunami excitation due to splay faulting has been proposed for the 1944 Mw 8.1 Tonankai earthquake in the Nankai Trough (Moore et al., 2007).
Section snippets
Tectonic setting and residual gravity anomaly
The Java subduction zone accommodates underthrusting of the Indo-Australian plate beneath Eurasia at approximately 67 mm/yr (Tregoning et al., 1994). The incoming plate in offshore western Java is structurally complex, hosting a dense population of seamounts and the Roo Rise oceanic plateau (Shulgin et al., 2011). The forearc is characterized by an outer-arc high, which typically extends 100 km from the trench-axis with water-depths of 2–3 km Kopp et al., 2002, Planert et al., 2010. Landward of
Seismic P-wave back-projection
We perform P-wave back-projection using the procedure described in Fan and Shearer (2015), using vertical-component velocity records from the International Federation of Digital Seismograph Networks (FDSN) seismic stations that are available and distributed by the Data Management Center (DMC) of the Incorporated Research Institutions for Seismology (IRIS). Because back-projection techniques do not make assumptions about fault geometry or rupture velocity, they are able to resolve complex
Tsunami tide gauge back-propagation
To constrain tsunami source locations, we perform tsunami back-propagation with five nearby tide gauges recording the tsunami of the 2006 Java earthquake (Fig. 5a). The tsunami waveforms are high-pass filtered at 2 h to remove tidal signals, from which the initial and first-crest arrivals are estimated (Table 1). With the first-crest arrivals, back-propagation of tsunami waves from the tide gauges is used to delineate possible source locations of sea surface displacements (Fig. 5b–f). We
Discussion
Tsunami waveform inversion suggests that the tsunami source of the 2006 Java earthquake was about 200 km long with the largest slip (∼2.5 m) stably located about 150 km east of the epicenter, regardless of the assumed earthquake rupture velocity (Fujii and Satake, 2006). This tsunami-derived slip model is significantly different from the seismic slip models Ammon et al., 2006, Bilek and Engdahl, 2007, Fujii and Satake, 2006, Yagi and Fukahata, 2011, Ye et al., 2016, which suggest the largest slip
Conclusions
The 2006 Mw 7.8 Java earthquake ruptured more than 200 km from west to east, lasting for more than ∼180 s. Finite-fault slip models suggest a smooth and slow rupture with the largest slip patch within ∼50 km away from the hypocenter Ammon et al., 2006, Bilek and Engdahl, 2007, Yagi and Fukahata, 2011, Ye et al., 2016, Ye et al., 2016, which is supported by our low-frequency back-projection results. In contrast, high-frequency global back-projection results suggest a two-stage rupture. The first
Acknowledgments
We thank the editor Dr. Kelin Wang and two reviewers for their constructive suggestions, which led to improvements in our paper. We would also like to thank Lingling Ye for sharing her finite-fault slip model. Finite-fault slip model of Yagi and Fukahata (2011) is downloaded from the Source Inversion Validation (SIV) database (SRCMOD, http://equake-rc.info/) (Mai et al., 2016). Finite-fault slip model obtained with both body and surface waves is downloaded from the U.S. Geological Survey
References (75)
- et al.
The global CMT project 2004–2010: centroid-moment tensors for 13,017 earthquakes
Phys. Earth Planet. Inter.
(2012) Mechanism of tsunami earthquakes
Phys. Earth Planet. Inter.
(1972)- et al.
Anatomy of the western Java plate interface from depth-migrated seismic images
Earth Planet. Sci. Lett.
(2009) - et al.
Smooth and rapid slip near the Japan trench during the 2011 Tohoku-Oki earthquake revealed by a hybrid back-projection method
Earth Planet. Sci. Lett.
(2012) - et al.
The 1994 Java tsunami earthquake: slip over a subducting seamount
J. Geophys. Res.
(2001) - et al.
The 17 July 2006 Java tsunami earthquake
Geophys. Res. Lett.
(2006) - et al.
Upper-plate controls on co-seismic slip in the 2011 magnitude 9.0 Tohoku-oki earthquake
Nature
(2016) - et al.
Gravity anomalies, crustal structure, and seismicity at subduction zones: 1. Seafloor roughness and subducting relief
Geochem. Geophys. Geosyst.
(2015) - et al.
Gravity anomalies, crustal structure, and seismicity at subduction zones: 2. Interrelationships between fore-arc structure and seismogenic behavior
Geochem. Geophys. Geosyst.
(2015) - et al.
A new asymptotic method for the modeling of near-field accelerograms
Bull. Seismol. Soc. Am.
(1984)
Rupture characterization and aftershock relocations for the 1994 and 2006 tsunami earthquakes in the Java subduction zone
Geophys. Res. Lett.
Applying wedge theory to dynamic rupture modeling of fault junctions
Bull. Seismol. Soc. Am.
Tsunami wave analysis and possibility of splay fault rupture during the 2004 Indian ocean earthquake
Pure Appl. Geophys.
Dynamics of the 2015 M7.8 Nepal earthquake
Geophys. Res. Lett.
Real-time W-phase inversion during the 2011 off the Pacific coast of Tohoku earthquake
Earth. Planets. Space.
An Introduction to the Bootstrap
Detailed rupture imaging of the 25 April 2015 Nepal earthquake using teleseismic P waves
Geophys. Res. Lett.
Local near instantaneously dynamically triggered aftershocks of large earthquakes
Science
Extreme runup from the 17 July 2006 Java tsunami
Geophys. Res. Lett.
Source of the July 2006 west Java tsunami estimated from tide gauge records
Geophys. Res. Lett.
Theoretical relationship between back-projection imaging and classical linear inverse solutions,
Geophys. J. Int.
Tsunami earthquakes and subduction processes near deep-sea trenches
Retracking Cryosat-2, Envisat and Jason-1 radar altimetry waveforms for improved gravity field recovery
Geophys. J. Int.
Rapid source characterization of the 2011 Mw 9.0 off the Pacific coast of Tohoku earthquake
Earth Planets Space
88 hours: The U.S. Geological Survey National Earthquake Information Center response to the 11 March 2011 Mw 9.0 Tohoku earthquake
Seismol. Res. Lett.
Slab1.0: A three-dimensional model of global subduction zone geometries
J. geophys. Res.
Shear and compressional velocity models of the mantle from cluster analysis of long-period waveforms
Geophys. J. Int.
On-Line Bulletin
Extent, duration and speed of the 2004 Sumatra-Andaman earthquake imaged by the Hi-net array
Nature
Update on CRUST1.0-A 1-degree global model of Earth's crust
Probabilistic imaging of tsunamigenic seafloor deformation during the 2011 Tohoku-oki earthquake
J. Geophys. Res.
Effects of prestress state and rupture velocity on dynamic fault branching
J. Geophys. Res
The 1992 Nicaragua earthquake: a slow tsunami earthquake
Nature
Traveltimes for global earthquake location and phase identification
Geophys. J. Int.
The 2010 Mw 8.8 Chile earthquake: triggering on multiple segments and frequency-dependent rupture behavior
Geophys. Res. Lett
Hidden aftershocks of the 2011 Mw 9.0 Tohoku, Japan earthquake imaged with the backprojection method
J. Geophys. Res.
Frequency-dependent rupture process of the 2011 Mw 9.0 Tohoku earthquake: comparison of short-period P wave backprojection images and broadband seismic rupture models
Earth Planets Space
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