Importance of horizontal seafloor motion on tsunami height for the 2011 Mw=9.0 Tohoku-Oki earthquake

Abstract It is now clear that the 2011 Tohoku-Oki earthquake ruptured the subduction interface all the way to the Japan Trench. However, there is significant disagreement about just how much slip occurred at the trench, with most geodetic studies locating only a small fraction of the maximum slip there, whereas broadband seismic studies put the majority of the slip near the trench. Measurements of seafloor displacement near the trench also imply more slip there than is estimated by the geodetic studies. Here, by means of a joint inversion of displacement measurements and seafloor pressure data, we show that it is possible to reconcile geodetic and seismic studies and that a considerable amount of slip indeed occurred at the trench, with slip magnitudes reaching 57–74% of the maximum slip. The seafloor displacement predicted by our model agrees very well with independent measurements made close to the trench. We also find good agreement between our tsunami model and independent measurements of tsunami height in the ocean and on land. Re-running of the inversion without the near-field pressure gauge data, however, leads to underprediction of the flooding on land, even when the seafloor geodetic data are still included. Thus, even if the seafloor geodetic measurements had been available in real time, they would still not have allowed reliable prediction of near-field tsunami inundation. Close to the trench, the dip of the plate interface is shallow, which serves to decrease the vertical motion of the sea floor for any given slip. However, the horizontal motion is conversely larger. Because the ocean floor slopes steeply near the trench, it acted like a giant wedge, converting the horizontal motion of the ground into an uplift of the water column and causing the peak initial tsunami wave height to be twice as high as it would have been from vertical displacement alone.

[1]  G. Panza,et al.  Viscoelastic relaxation and long‐lasting after‐slip following the 1997 Umbria‐Marche (Central Italy) earthquakes , 2007 .

[2]  Gregory C. Beroza,et al.  Shallow Dynamic Overshoot and Energetic Deep Rupture in the 2011 Mw 9.0 Tohoku-Oki Earthquake , 2011, Science.

[3]  T. Furumura,et al.  Significant tsunami observed at ocean-bottom pressure gauges during the 2011 off the Pacific coast of Tohoku Earthquake , 2011 .

[4]  Thorne Lay,et al.  Inversion of high‐rate (1 sps) GPS data for rupture process of the 11 March 2011 Tohoku earthquake (Mw 9.1) , 2011 .

[5]  W. K. Hastings,et al.  Monte Carlo Sampling Methods Using Markov Chains and Their Applications , 1970 .

[6]  Geoffrey Blewitt,et al.  Fixed point theorems of GPS carrier phase ambiguity resolution and their application to massive network processing: Ambizap , 2008 .

[7]  Kenji Satake,et al.  Tsunami source of the 2011 off the Pacific coast of Tohoku Earthquake , 2011 .

[8]  Narumi Takahashi,et al.  The 2011 Tohoku-Oki Earthquake: Displacement Reaching the Trench Axis , 2011, Science.

[9]  F. LeMoine,et al.  A reassessment of global and regional mean sea level trends from TOPEX and Jason‐1 altimetry based on revised reference frame and orbits , 2007 .

[10]  H. Kanamori,et al.  Possible large near-trench slip during the 2011 Mw 9.0 off the Pacific coast of Tohoku Earthquake , 2011 .

[11]  Sarah E. Minson,et al.  The 2011 Magnitude 9.0 Tohoku-Oki Earthquake: Mosaicking the Megathrust from Seconds to Centuries , 2011, Science.

[12]  Chihiro Hashimoto,et al.  Interplate seismogenic zones along the Kuril–Japan trench inferred from GPS data inversion , 2009 .

[13]  Kenji Satake,et al.  Tsunami generation by horizontal displacement of ocean bottom , 1996 .

[14]  Y. Ito,et al.  Tsunami source of the 2011 Tohoku‐Oki earthquake, Japan: Inversion analysis based on dispersive tsunami simulations , 2011 .

[15]  J. Jackson,et al.  Tsunami earthquake generation by the release of gravitational potential energy , 2012 .

[16]  Nobuhito Mori,et al.  Survey of 2011 Tohoku earthquake tsunami inundation and run‐up , 2011 .

[17]  Guus S. Stelling,et al.  A staggered conservative scheme for every Froude number in rapidly varied shallow water flows , 2003 .

[18]  N. D’Agostino,et al.  Clues from joint inversion of tsunami and geodetic data of the 2011 Tohoku-oki earthquake , 2012, Scientific Reports.

[19]  P. Segall,et al.  Seismic and aseismic fault slip before and during the 2011 off the Pacific coast of Tohoku Earthquake , 2011 .

[20]  Sin-Iti Iwasaki,et al.  Experimental Study of a Tsunami Generated by a Horizontal Motion of a Sloping Bottom , 1982 .

[21]  T. Wright,et al.  Real‐time, reliable magnitudes for large earthquakes from 1 Hz GPS precise point positioning: The 2011 Tohoku‐Oki (Japan) earthquake , 2012 .

[22]  Aditya Riadi Gusman,et al.  Source model of the great 2011 Tohoku earthquake estimated from tsunami waveforms and crustal deformation data , 2012 .

[23]  Masataka Ando,et al.  Evidence of large scale repeating slip during the 2011 Tohoku‐Oki earthquake , 2011 .

[24]  W. J. F. Simons,et al.  Sea level change in the Gulf of Thailand from GPS-corrected tide gauge data and multi-satellite altimetry , 2011 .

[25]  Y. Okada.  Surface deformation due to shear and tensile faults in a half-space , 1985 .

[26]  Albert Tarantola,et al.  Monte Carlo sampling of solutions to inverse problems , 1995 .

[27]  Tomokazu Kobayashi,et al.  Coseismic and postseismic slip of the 2011 magnitude-9 Tohoku-Oki earthquake , 2011, Nature.

[28]  Kaj M. Johnson,et al.  A Fully Bayesian Inversion for Spatial Distribution of Fault Slip with Objective Smoothing , 2008 .

[29]  Kinjiro Kajiura,et al.  The Leading Wave of a Tsunami , 1963 .

[30]  Propagation and Inundation Characteristics of the 2011 Tohoku Tsunami on the Central Sanriku Coast , 2012 .

[31]  Akira Asada,et al.  Displacement Above the Hypocenter of the 2011 Tohoku-Oki Earthquake , 2011, Science.

[32]  N. Takahashi,et al.  Confirming sharp bending of the Pacific plate in the northern Japan trench subduction zone by applying a traveltime mapping method , 2006 .

[33]  Richard G. Gordon,et al.  Geologically current plate motions , 2010 .

[34]  J. Zumberge,et al.  Precise point positioning for the efficient and robust analysis of GPS data from large networks , 1997 .

[35]  T. Iinuma,et al.  Coseismic slip distribution of the 2011 off the Pacific coast of Tohoku Earthquake (M 9.0) estimated based on GPS data—Was the asperity in Miyagi-oki ruptured? , 2011 .

[36]  Vasily V. Titov,et al.  Real-Time Tsunami Forecasting: Challenges and Solutions , 2003 .

[37]  Guus S. Stelling,et al.  A finite volume analogue of the P1NC-P1 finite element: With accurate flooding and drying , 2010 .

[38]  Z. Altamimi,et al.  ITRF2005 : A new release of the International Terrestrial Reference Frame based on time series of station positions and Earth Orientation Parameters , 2007 .

[39]  D. Vatvani,et al.  Defining the source region of the Indian Ocean Tsunami from GPS, altimeters, tide gauges and tsunami models , 2007 .

[40]  F. Sigmundsson,et al.  Increased capture of magma in the crust promoted by ice-cap retreat in Iceland , 2011 .

[41]  C. Rizos,et al.  The International GNSS Service in a changing landscape of Global Navigation Satellite Systems , 2009 .

[42]  Motoyuki Kido,et al.  Frontal wedge deformation near the source region of the 2011 Tohoku‐Oki earthquake , 2011 .

[43]  F. Imamura,et al.  The 869 Jogan tsunami deposit and recurrence interval of large-scale tsunami on the Pacific coast of northeast Japan , 2001 .