Tsunamigenic Major and Great Earthquakes

T Tsunamigenic Major and Great surface is inclined, the rock Earthquakes (2004–2013): Source masses above and below the Processes Inverted from Seismic, fault are termed hanging wall Geodetic, and Sea-Level Data and footwall, respectively Hypocenter The position (longitude, latitude, depth) of the S. Lorito1, F. Romano1 and T. Lay2 earthquake nucleation point 1Roma 1, Sez. Sismologia e Tettonofisica, Istituto Rake (or Slip The angle of the relative Nazionale di Geofisica e Vulcanologia, Roma, Direction) displacement between the Italy hanging wall and the footwall 2Department of Earth and Planetary Sciences, of a fault during an earthquake University of California Santa Cruz, Santa Cruz, measured in the fault surface CA, USA relative to the horizontal strike direction Glossary Strike The angle, measured relative to north, of the intersection (trace) of the earthquake fault Earthquake Location and Fault ’ Parameters with the Earth s surface Faulting Style Dip The angle between the Earth’s Normal Fault Fault where the hanging wall horizontal surface and the moves down with respect to the earthquake fault footwall Epicenter The position (longitude, Reverse Fault Fault where the hanging wall latitude) of the hypocenter moves up with respect to projected on the Earth’s surface the footwall; if the dip angle is Earthquake The fracture within a rock <= 45, it is termed a thrust Fault volume that separates two rock fault masses where there is evidence Strike-Slip Fault (often steeply dipping) of a relative displacement (slip) Fault where the two blocks separated between them during an by the fault surface move earthquake; the surface where horizontally along the fault trace the slip occurred is termed the relative to each other; if the fault surface; if the fault # Springer Science+Business Media New York 2015 R.A. Meyers (ed.), Encyclopedia of Complexity and Systems Science, DOI 10.1007/978-3-642-27737-5_641-1 2 Tsunamigenic Major and Great Earthquakes (2004–2013) À motion of the block across the M ¼ 2 ðÞÀM : w 3 log 0 10 73, fault trace from an observer withM0 in dyne Ã cmÞ moves toward left, the Rigidity Shear stress to shear strain mechanism is termed left (or Shear ratio of a material; this lateral, otherwise the Modulus) coefficient is used to measure mechanism is termed right the stiffness of a material and lateral describe its response to Transpressive Reverse fault with an oblique applied shear stress; in Fault rake component subduction zone Kinematic Rupture Parameters environments, the rigidity and Inversion varies with depth, with lower values in the shallow Inversion A procedure that uses a set of sedimentary part of the (or Inverse direct or indirect megathrust Problem) observations to retrieve the Seismic Moment A scalar measure of the parameters of a model that is earthquake size based on the consistent with the rupture area (A), the average observations; this is a slip (D) on the fault surface, common approach (many and the rigidity (m) of the techniques are used medium surrounding the depending on the problem to fault; the relationship among be solved) in seismology to these parameters is retrieve earthquake M0 ¼ A Ã D Ã m kinematic parameters such Seismic Cycle as the seismic moment, slip distribution, and rupture Coseismic The interval in which the velocity Phase accumulated stress on the fault Rupture Area Portion of the fault surface is suddenly released causing an that slips during an earthquake earthquake Interseismic The capability of accumulating Rupture Velocity Velocity at which the rupture Coupling stress on a fault in the period that front propagates over the separates two large seismic fault surface during an events (interseismic phase); earthquake; it may be very strongly coupled (or locked) irregular spatially faults accumulate stress at the Slip Distribution Pattern that describes the rate at which the plates are earthquake rupture in terms moving relative to each other of timing and amount of slip and, in principle, are more prone along the fault surface to host large earthquakes Earthquake Size Postseismic The interval in which additional Phase slip or viscoelastic relaxation Moment Measure of earthquake occurs after the mainshock as Magnitude magnitude computed using effect of the stress and strain the seismic moment,M0, redistribution estimated from various Seismic Cycle The three phases involving the methods process of stress and strain buildup (interseismic), release Tsunamigenic Major and Great Earthquakes (2004–2013) 3 (coseismic), and redistribution Tsunami The difference, computed on a (postseismic) that occurs along Amplitude tsunami waveform, between the the fault surface before, during, peak of the tsunami wave and the and after an earthquake, undisturbed sea-level value respectively; each phase occurs Tsunami The difference, computed on a with a very different time scale Height tsunami waveform, between (many years for interseismic, successive crest and trough seconds for coseismic, from values of a tsunami wave minutes to months for Tsunami The time between two postseismic) Period successive tsunami wave Strain Is the deformation of a rock extrema (generally considering mass subjected to tectonic the crest of the wave) that is the stresses amount of time taken by a Stress Is the force per unit area applied tsunami wave to complete a on a surface (e.g., a fault cycle surface) within a volume Tsunami The distance between two Subduction Wavelength consecutive tsunami waves (generally considering the crest Megathrust An extremely large thrust fault, of the wave) formed along a subduction zone plate boundary, hosting very large Definition of the Subject earthquakes Subduction Convergence zone of two tectonic The decade 2004–2013 was characterized by an Zone plates where one plate moves unusually large rate (1.7 per year) of great earth- beneath the other; the contact quakes (MW 8) (Lay 2015). The majority surface between the two occurred on subduction zone megathrusts. Signif- convergent plates is termed the icant tsunamis were generated by most of them, as subduction interface or well as by several major (MW 7.0–7.9) earth- megathrust; subduction zones are quakes at very shallow depth on megathrusts, or the most seismically active by great intraplate normal faulting events near environments on Earth and where subduction zones. most of the largest earthquakes Two of the great events, the 2004 Sumatra- occur Andaman MW 9.2 and the 2011 Tohoku MW 9.0 Trench The deep bathymetric trough earthquakes are, respectively, the third and the position where the subducting fourth largest earthquakes seismologically recorded plate begins to descend beneath (since 1900) and the largest events of the last the overriding plate 50 years (http://earthquake.usgs.gov/earthquakes/ Wedge The shallow portion of the world/10_largest_world.php). These events were overriding plate characterized by larger than had been anticipated for their source the accumulation of sedimentary regions and produced two of the most damaging material due to the collision with tsunamis in modern times. It is now widely the subducting plate accepted that great tsunamigenic earthquakes may Tsunami occur in most subduction zones worldwide, although very infrequently in some regions (e.g., Run-up The maximum topographic Stein and Okal 2011; Kagan and Jackson 2013). elevation reached by the tsunami The occurrence of many important seismic during the inundation events during a time of greatly expanded global 4 Tsunamigenic Major and Great Earthquakes (2004–2013) seismological, geodetic, and tsunami recording than previously observed (Lay 2015). Most of systems has provided the scientific community these great earthquakes occurred near the Pacific with an unprecedented set of geophysical obser- and Indian Plate boundary margins where previ- vations. Data availability has prompted the devel- ous great earthquakes have occurred, but 40 % opment of new data inversion techniques for ruptured within lithospheric plates rather than reconstruction and understanding of the space- directly on plate boundaries, and the location of time fault sliding process during the earthquake, the latter events could not be directly anticipated which, in turn, provides a better understanding of based on plate motions. Even for the plate bound- the resulting tsunamigenic potential. ary events, some of the ruptures had surprising We address most of the major and great spatial extent and features of their slip distribu- tsunamigenic earthquakes that occurred over the tion, as well as nature of the tsunamis they decade. The objective of this entry is to discuss the generated. general features of source models – as retrieved by The overall size of the 2004 MW 9.2 Sumatra- inversion of seismic, geodetic, and tsunami Andaman 2004 megathrust earthquake had not data – and of the observed tsunamis. We highlight been anticipated for the region along on the the kinematic complexity of the rupture processes Sunda Trench from Northern Sumatra to the in subduction zones and the relation between fault Andaman Islands. This was due in part to the slip distribution, bathymetry, and coastal features lack of knowledge of its subsequently discovered on one hand and the observed tsunami impacts on middle-ages predecessors (Sieh et al. 2015 and the other hand. references therein) and in part because of widely accepted assumptions about the seismic potential of the highly oblique convergence of oceanic lith- Introduction osphere along this plate boundary. The rupture length (>1300 km) and

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