Slip Area Research Articles

Kinematic Rupture Model and Hypocenter Relocation of the 2013 Mw 6.6 Lushan Earthquake Constrained by Strong-Motion and Teleseismic Data

Online Material: Tables of 1D velocity structure, hypocentral locations, and kinematic rupture model. On 20 April 2013, an M w 6.6 earthquake struck Lushan, Sichuan province, China (hereafter as Lushan earthquake), which caused 196 deaths and 21 missing. As another disastrous earthquake occurred on the Longmenshan fault after the 2008 M w 7.9 Wenchuan earthquake, the Lushan earthquake stimulated an extensive discussion about its seismogenesis. In particular, whether it was a large aftershock of the 2008 M w 7.9 Wenchuan earthquake has been heatedly debated (Chen et al. , 2013; Du et al. , 2013; Liu, Yi, et al. , 2013; Wang et al. , 2013; Jia et al. , 2014). Actually, after the Wenchuan earthquake, an increased seismic hazard for the southwest of the Longmenshan fault has been commonly recognized (Parsons et al. , 2008; Toda et al. , 2008). The occurrence of the Lushan earthquake seems to have confirmed this common understanding, and further attracts attention on the re‐evaluation of future seismic activities on the southwest Longmenshan fault (Chen et al. , 2013). As the basis of these discussions, the source characteristics of the Lushan earthquake need to be well understood. As a routine work for fast source earthquake information, Zhang et al. (2013) released the preliminary teleseismic rupture model about three hours after the Lushan earthquake. Their results show that the earthquake has no dominant rupture direction. The major slip area is located around the hypocenter and does not reach the surface. It is known, however, that teleseismic data can only constrain the ruptured area relatively to the hypocenter (rupture initiation point). In contrast, near‐field strong‐motion data can provide information useful in precisely and accurately locating …

Effect of patchwise slip on fluid flow

In this paper, we show that large connected slip patches (hydrophobic patches) are a necessity to induce macroscopic slip effects of water flow in microchannels. For this purpose, the 2D fluid flow between a planar stationary surface with alternating stick and slip patches and a parallel planar surface moving with a constant relative velocity has been studied by computer simulations based on Navier-Stokes equations. A slip patch is defined as the slipping length in a 2D system or a slip area of the surface in a 3D system. The simulations reveal that the ratio (size of each slip patch)/(distance between the two parallel interfaces) has profound effect on the viscous stress on the moving surface when this ratio is around and above one. However, when the ratio is much below one, the effect of the slip patches are minor, even if the area fraction of slip patches are higher than 50 %. Obviously, the stick patches adjacent to the slip patches act as effective barriers, preventing the fluid velocity to increase near the surface with alternating stick and slip patches. The obtained results are scalable and applicable on all length scales, with an exception for narrow channels in the subnano regime, i.e. < 1 nm where specific effects as the atomistic composition and the nanostructure of the wall as well as the interactions between the wall and the water molecules have an effect.

Creep force modelling for rail traction vehicles based on the Fastsim algorithm

The evaluation of creep forces is a complex task and their calculation is a time-consuming process for multibody simulation (MBS). A methodology of creep forces modelling at large traction creepages has been proposed by Polach [Creep forces in simulations of traction vehicles running on adhesion limit. Wear. 2005;258:992–1000; Influence of locomotive tractive effort on the forces between wheel and rail. Veh Syst Dyn. 2001(Suppl);35:7–22] adapting his previously published algorithm [Polach O. A fast wheel–rail forces calculation computer code. Veh Syst Dyn. 1999(Suppl);33:728–739]. The most common method for creep force modelling used by software packages for MBS of running dynamics is the Fastsim algorithm by Kalker [A fast algorithm for the simplified theory of rolling contact. Veh Syst Dyn. 1982;11:1–13]. However, the Fastsim code has some limitations which do not allow modelling the creep force – creep characteristic in agreement with measurements for locomotives and other high-power traction vehicles, mainly for large traction creep at low-adhesion conditions. This paper describes a newly developed methodology based on a variable contact flexibility increasing with the ratio of the slip area to the area of adhesion. This variable contact flexibility is introduced in a modification of Kalker's code Fastsim by replacing the constant Kalker's reduction factor, widely used in MBS, by a variable reduction factor together with a slip-velocity-dependent friction coefficient decreasing with increasing global creepage. The proposed methodology is presented in this work and compared with measurements for different locomotives. The modification allows use of the well recognised Fastsim code for simulation of creep forces at large creepages in agreement with measurements without modifying the proven modelling methodology at small creepages.

Finite-Difference Simulation of Long-Period Ground Motion for the Nankai Trough Megathrust Earthquakes

We evaluated long-period ground motions for the anticipated Nankai Trough megathrust earthquake in southwest Japan. To understand a variation of longperiod ground motions caused by the uncertainty of the source model, we performed a finite difference simulation using 104 source models, assuming various possible source parameters, including rupture area, asperity configuration, and hypocenter location. For the variety of rupture areas, we included scenarios that have extremely huge rupture areas, as was proposed by the Japan Central Disaster Management Council of Cabinet Office after the 2011 Tohoku-Oki earthquake. We also included scenarios that have large slip areas near the trough following the lessons learned from the 2011 event. Simulated waveforms and response spectra show a large variation at a site. However, by grouping the simulation results with respect to the source area, we determined that scenarios with wider rupture areas have a larger peak ground velocity and velocity response than those with smaller rupture areas. The influence of the large slip near the trough causes later phases to be large and long. However, the later phases are decreased by using a boxcarlike slip velocity time function instead of a Kostrovlike function and by decreasing rupture velocity. The spatial distribution of the simulated peak ground velocity and velocity response show that the long-period ground motions are amplified particularly on sedimentary basins, where big cities have been established. It is important to consider how to account for the large variation of the simulation results in the seismic hazard assessment.

Rapid pulses of uplift, subsidence, and subduction erosion offshore Central America: Implications for building the rock record of convergent margins

Integrated Ocean Drilling Program (IODP) Expedition 334 to southern Costa Rica, Central America, documented unprecedented subduction erosion in an area of active seismic slip. Widespread subduction erosion of the upper plate initiated when the Cocos Ridge, an overthickened aseismic ridge, arrived at the Middle America Trench. Subduction erosion was coeval with the rapid formation of deposition centers on the forearc of the upper plate. The completely recovered shelf sequence constrains a short (<2 m.y.) interval of extreme subsidence (∼1200 m) with a rapid pulse occurring during the first ∼0.3 m.y. This event removed an estimated 1.2 × 106 km3 of forearc material at a rate of ∼1690 km3/m.y./km of trench during a time of rapid (∼1035 m/m.y.) shelf sediment accumulation. At this erosive margin, a sediment-starved trench persisted, in spite of abundant sediment supply, because subduction erosion led to the creation of forearc basins. Similar rapid pulses of subduction erosion may punctuate the evolution of many margins, contributing disproportionately to crustal recycling at subduction zones with implications for the evolution of continental crust and mountain belts, and recycling of continental material into the mantle.

Depth extent of the long‐term slow slip event in the Tokai district, central Japan: A new insight

Temporal changes to interplate coupling and long‐term aseismic slip in the Tokai Region of central Japan from July 1996 to June 2009 are statically inverted using continuous Global Positioning System (GPS) data and leveling observations, and examined using a new interpretation of aseismic slip. In this interpretation, the interplate coupling and the aseismic slip should be inferred and compared with reference to a state of no coupling on the plate interface rather than assuming steady state interplate coupling before the occurrence of the aseismic event as previous works have done. For this purpose, we used original time series data without subtracting any linear trends. The inferred distribution shows that the entire period can be divided into three subperiods based on the existence of the aseismic slip area from 2000 to 2005. The strength of the interplate coupling does not change throughout the observed period even though the distribution narrows along the dip direction after the aseismic slip terminates. The aseismic slip area inferred in this study, based on the no‐coupling reference, was determined to be deeper than the area where the long‐term slow slip event (SSE), defined as the slip corresponding to the residual displacement from the steady state, was hypothesized to have occurred in numerous previous studies. The total seismic moment released by the aseismic slip is equivalent to a Mw∼6.6 earthquake while the SSE in previous works was considered to be equivalent to a Mw∼7.0 to 7.1 earthquake. This difference can be attributed primarily to the effects on the interplate coupling, which previous studies did not take into account when defining the SSE. The aseismic slip area coincides well with the distribution of other types of plate interactions, such as short‐term slow slip events and low‐frequency earthquakes.

Repeated large Slow Slip Events at the southcentral Alaska subduction zone

We identify and study an ongoing Slow Slip Event (SSE) in the southcentral Alaska subduction zone using GPS measurements. This is the second large SSE in this region since modern geodetic measurements became available in 1993. We divide the ongoing SSE into two phases according to their transient displacement time evolution; their slip distributions are similar to each other but slip rates are slightly different. This ongoing SSE occurs downdip of the main asperity that ruptured in the 1964 Alaska earthquake, on the same part of the subduction interface as the earlier 1998–2001 SSE. The average slip rate of this SSE is ∼4–5cm/yr, with a cumulative moment magnitude of Mw 7.5 (Mw 7.3 and Mw 7.1 For Phases I and II, respectively) through the end of 2012. The time and space dependence of the GPS displacements suggest that the slip area remained nearly the same during Phase I, while the slip rate increased with time. The SSEs occur on a transitional section of the subduction plate interface between the fully locked updip part and the freely slipping deeper part. During the 1964 earthquake, slip on the region of the SSE was much lower than slip in the updip region. Based on this observation and the repeated SSEs, we conclude that this part of the interface slips repeatedly in SSEs throughout the interseismic period and does not build up a large slip deficit to be released through large slip in earthquakes.

Source‐rupture process of the 2011 Ibaraki‐oki, Japan, earthquake (Mw 7.9) estimated from the joint inversion of strong‐motion and GPS Data: Relationship with seamount and Philippine Sea Plate

AbstractThe source‐rupture process of the 2011 Ibaraki‐oki earthquake was estimated from the joint inversion of the strong‐motion and global positioning system (GPS) data. The estimated seismic moment and maximum slip are 7.8 × 1020 Nm (Mw 7.9) and 6.3 m, respectively. The total rupture duration is approximately 30 s. The derived source model has one large slip area, which is surrounded by the subducted seamount and the northeastern edge of the Philippine Sea plate. From this model, we concluded that the rupture propagation of the 2011 Ibaraki‐oki earthquake was stopped by the seamount and the Philippine Sea plate. We also showed the possibility of the rupture of this event being the reactivation of the preexisting asperity of an event that occurred in 1923.

High‐speed rupture in the first 20 s of the 2011 Tohoku earthquake, Japan

AbstractThe 2011 Tohoku earthquake produced tens of meters of fault slip near the Japan Trench, which generated devastating tsunami. The rupture process before the huge slip is still unclear due to a lack of resolution. Here I perform a multiscale slip inversion analysis to examine the first 10 and 20 s of the rupture process and the whole rupture process at different scales. The result shows that 4 s after the initiation, this earthquake started with a relatively high‐speed rupture that had a peak slip rate faster than 1 m/s and a rupture velocity comparable to 3 km/s. Fourteen seconds after the initiation, the rupture propagation direction changed from northward to westward, near the edge of the M 7.3 foreshock coseismic slip area. The stress release by the foreshock may contribute to the complex small‐scale rupture propagation, which may appear to be slow rupture propagation when only looking at long‐period data.

Pre- and postseismic slow slip surrounding the 2011 Tohoku-oki earthquake rupture

Slow (aseismic) slip that accommodates part of the long-term plate motion on subduction megathrusts is thought to be strongly related to the occurrence of large earthquakes on the same fault zone. However, the temporal evolution and spatial distribution of the aseismic slip before major earthquakes and of accelerated postseismic afterslip are largely unconstrained. We estimate cumulative offsets of small repeating earthquakes that are interpreted to reflect the in situ aseismic slip history on the subduction zone offshore northeastern Japan. These data reveal contrasting aseismic slip patterns between the coseismic rupture area of the Mw 9.0 Tohoku-oki earthquake and surrounding portions of the subduction thrust. The rupture area is characterised by low and variable slip rates before 2008, and the slip stopped almost completely after the earthquake. The region surrounding the rupture area exhibited higher aseismic fault slip rates before the earthquake and clear postseismic slip of up to 1.6m within 9 months following the main shock. The frictional fault properties and complete relief of ambient stress in the central rupture zone of the main shock probably control the observed distribution. The postseismic slip shows a more abrupt increase in the region closer to the source, suggesting outwards propagation of afterslip. Small but distinct increases in the slip rate in the ~3yr before the earthquake near the area of large coseismic slip suggests preseismic unfastening of the locked area in the last stage of the earthquake cycle.

Documenting five years of landsliding after the 2005 Kashmir earthquake, using repeat photography

The 8 October 2005 Kashmir earthquake triggered thousands of landslides at different scales through the Hazara–Kashmir region of northern Pakistan. A landslide inventory was prepared within a few months after the earthquake, which included detailed photographs and studies of landslides at 164 locations. Photographs were retaken in 2006 at all the 2005 locations and at selected 68 landslide locations in 2007. In 2010, 123 of the 2005 landslide locations in the inventory were reexamined and photographed again. Existing literature predicted that extensive landsliding, particularly under wet conditions, was likely to occur in the region in the years immediately following the earthquake. Surprisingly, the repeat studies revealed that the total landslide area increased only slightly over the five-year period of study, even given a particularly heavy monsoon rainfall season in 2006, with 46% of the locations showing little or no increase and 10% showing a noticeable increase in landsliding; in 44% of the locations vegetation growth was significant or complete within the exposed landslide slip area. Many of the new or reactivated failures occurred along roads and rivers, particularly along steeper slopes. We conclude that the landscape returned to equilibrium within only a few years after the earthquake. Nevertheless, a potential for future slope instability and landsliding in the region still exists. Hence continuation of landslide monitoring and risk assessment is still important for hazard mitigation in this region.

Numerical modelling of post-seismic rupture propagation after the Sumatra 26.12.2004 earthquake constrained by GRACE gravity data

In the last decades, the development of the surface and satellite geodetic and geophysical observations brought a new insights into the seismic cycle, documenting new features of inter-, co-, and post-seismic processes. In particular since 2002 satellite mission GRACE provides monthly models of the global gravity field with unprecedented accuracy showing temporal variations of the Earth's gravity field, including those caused by mass redistribution associated with earthquake processes. When combined with GPS measurements, these new data have allowed to assess the relative importance of afterslip and viscoelastic relaxation after the Sumatra 26.12.2004 earthquake. Indeed the observed post-seismic crustal displacements were fitted well by a viscoelastic relaxation model assuming Burgers body rheology for the asthenosphere (60–220 km deep) with a transient viscosity as low as 4 × 10^17 Pas and constant ~ 10^19 Pas steady state viscosity in the 60–660-km depth range. However, even the low-viscosity asthenosphere provides the amplitude of strain which gravity effect does not exceed 50 per cent of the GRACE gravity variations, thus additional localized slip of about 1 m was suggested at downdip extension of the coseismic rupture. Post-seismic slip at coseismic rupture or its downdip extension has been suggested by several authors but the mechanism of the post-seismic fault propagation has never been investigated numerically. Depth and size of localized slip area as well as rate and time decay during the post-seismic stage were either assigned a priory or estimated by fitting real geodesy or gravity data. In this paper we investigate post-seismic rupture propagation by modelling two consequent stages. First, we run a long-term, geodynamic simulation to self-consistently produce the initial stress and temperature distribution. At the second stage, we simulate a seismic cycle using results of the first step as initial conditions. The second short-term simulation involves three substeps, including additional stress accumulation after part of the subduction channel was locked; spontaneous coseismic slip; formation and development of damage zones producing afterslip. During the last substep post-seismic stress leads to gradual ~1 m slip localized at three faults around ~100-km downdip extension of the coseismic rupture. We used the displacement field caused by the slip to calculate pressure and density variations and to simulate gravity field variations. Wavelength of calculated gravity anomaly fits well to that of the real data and its amplitude provides about 60 per cent of the observed GRACE anomaly. Importantly, the surface displacements caused by the estimated afterslip are much smaller than those registered by GPS networks. As a result cumulative effect of Burgers rheology viscoelastic relaxation (which explains measured GPS displacements and about a half of gravity variations) plus post-seismic slip predicted by damage rheology model (which causes much smaller surface displacements but provides another half of the GRACE gravity variations) fits well to both sets of the real data. Hence, the presented numerical modelling based on damage rheology supports the process of post-seismic downdip rupture propagation previously hypothesized from the GRACE gravity data.

An interpretation of tsunami earthquake based on a simple dynamic model: Failure of shallow megathrust earthquake

The 2011 Tohoku earthquake demonstrated that extremely large seismic slip can occur at shallow plate interfaces in subduction zones. The large slip area for the Tohoku earthquake included the source region of a tsunami earthquake. We performed dynamic rupture simulations using simplified fault models and the mechanism of thermal fluid pressurization. We found that small fluctuations of initial shear stress near a trench, within 1 MPa, lead to differences in seismic moment release greater than two orders of magnitude. In addition, we performed another experiment varying rupture nucleation sizes and obtained similar acute sensitivities of parameters. Moderate slip events with trapezoidal (flat‒topped) source time functions appear to occupy a transition position, between shallow megathrust earthquakes with surface rupture and smaller ordinary earthquakes without surface rupture. We interpret this result as representing the differences in interplate slip between shallow megathrust earthquakes, tsunami (moderate) earthquakes, and non‒tsunami (ordinary) earthquakes, on the basis of seismic observations.

Segmentation of the Vp/Vs ratio and low‐frequency earthquake distribution around the fault boundary of the Tonankai and Nankai earthquakes

[1] Beneath the Kii Peninsula, the distribution of low-frequency earthquakes (LFEs) forms three clusters. A previous study shows that one of the clusters has anomalously less amount of cumulative slip than the others. To understand the cause of this variation, we applied a tomographic analysis using arrival times of earthquakes recorded by both ocean bottom seismometers and onshore stations. As a result, we identified segmentation about the Vp/Vs ratio around the subducting plate interface corresponding to the distribution of LFEs. One of the segments has low a Vp/Vs ratio that coincides with the small-slip LFE cluster. Another segment has a high Vp/Vs ratio in which almost no LFEs occur. We conclude that the relatively low pore fluid pressure within the low Vp/Vs segment contributes to the small-slip LFE cluster and that the gap of LFEs within the high Vp/Vs segment corresponds to stable slip area due to high pore fluid pressure.

Finite-Fault Source Inversion Using Teleseismic P Waves: Simple Parameterization and Rapid Analysis

We examine the ability of teleseismic P waves to provide a timely image of the rupture history for large earthquakes using a simple, 2D finite‐fault source parameterization. We analyze the broadband displacement waveforms recorded for the 2010 M w∼7 Darfield (New Zealand) and El Mayor‐Cucapah (Baja California) earthquakes using a single planar fault with a fixed rake. Both of these earthquakes were observed to have complicated fault geometries following detailed source studies conducted by other investigators using various data types. Our kinematic, finite‐fault analysis of the events yields rupture models that similarly identify the principal areas of large coseismic slip along the fault. The results also indicate that the amount of stabilization required to spatially smooth the slip across the fault and minimize the seismic moment is related to the amplitudes of the observed P waveforms and can be estimated from the absolute values of the elements of the coefficient matrix. This empirical relationship persists for earthquakes of different magnitudes and is consistent with the stabilization constraint obtained from the L‐curve in Tikhonov regularization. We use the relation to estimate the smoothing parameters for the 2011 M w 7.1 East Turkey, 2012 M w 8.6 Northern Sumatra, and 2011 M w 9.0 Tohoku, Japan, earthquakes and invert the teleseismic P waves in a single step to recover timely, preliminary slip models that identify the principal source features observed in finite‐fault solutions obtained by the U.S. Geological Survey National Earthquake Information Center (USGS/NEIC) from the analysis of body‐ and surface‐wave data. These results indicate that smoothing constraints can be estimated a priori to derive a preliminary, first‐order image of the coseismic slip using teleseismic records.

The 2010 Maule, Chile, Coseismic Gap and Its Relationship to the 25 March 2012 Mw 7.1 Earthquake

Abstract A backprojection method is applied to the 27 February 2010 M w 8.8 and 25 March 2012 M w 7.1 Maule, Chile, earthquakes using high‐frequency (0.8–2 Hz) USArray data. During the 2010 event, highest energy release occurred north of the epicenter, with two subevents comprising this rupture. The gap between these subevents was about 100 km and 15 s, suggesting that P waves from the first subevent dynamically triggered the second subevent. This triggering can be explained as a consequence of stopping phases generated at the terminus of subevent 1, as the rupture encounters a region of low interseismic coupling. This argument is supported by the occurrence of the 2012 M w 7.1 event, which is the largest interface earthquake since the 2010 mainshock and ruptured an area that completely filled the gap left from the mainshock. Seismic gaps, regions between the slip areas of past giant earthquakes, are known to have a higher potential for generating future large events. The results of this study show that a coseismic gap behaves similarly, and detailed imaging of rupture propagation can be used to identify areas that may produce large earthquakes. A comparable coseismic gap to the 2010 Chile gap is identified for the 2011 M w 9.0 Tohoku, Japan, earthquake that may be the site of a large event in the near future. Online Material: Figures showing point source synthetic tests for the back projection method, station location, and distribution of energy release.

Spatial and temporal evolution of the long-term slow slip in the Bungo Channel, Japan

The Global Positioning System network in Japan detected a transient in the Bungo Channel, Japan, in 2009. Time-dependent analysis suggests that between May and September 2009, an aseismic slip might occur beneath the Bungo Channel and southwest Shikoku. From September 2009 to January 2010, the slip area shifted toward southwest Shikoku. Since approximately March 2010, the slip has increased in magnitude and speed while expanding into the Bungo Channel. The estimated rupture process is similar to those of previous Bungo Channel slow slips, in that the slip starts in a shallower region and expands into a deeper region with the acceleration of the slip. The high-speed period of the 2010 event corresponds to a marked increase in the activity of low-frequency earthquakes, similar to that of the 2003 event. The total slip distribution of the 2010 event is similar to that of previous long-term Bungo slow slips, verifying the hypothesis that long-term slow slips are characteristic events in the Bungo Channel.

Imaging of the subducted Kyushu-Palau Ridge in the Hyuga-nada region, western Nankai Trough subduction zone

We performed 3D seismic tomography of the Hyuga-nada region, western Nankai subduction zone, to investigate the relationship of the subducted part of Kyushu-Palau Ridge (KPR) to coseismic rupture propagation, seismicity, and shallow very low frequency earthquakes. Combining active-source and passive-source data recorded both onshore and offshore, we imaged the deep slab from near the trough axis to the coastal area. Our results show the subducted KPR as a low-velocity belt oriented NW–SE extending down the plate boundary to around 30km depth. At this depth, we suggest that the subducted KPR detaches from the slab and becomes underplated on the overriding continental plate. As the coseismic slip areas of past large earthquakes do not extend into the subducted KPR, we suggest that it may inhibit rupture propagation. The interior of the subducted KPR shows active intraslab seismicity with a wide depth distribution. Shallow very low frequency earthquakes are continuously active above the location of the subducted KPR, whereas they are intermittent to the northeast of the subducted KPR. Thus, the subducted KPR appears to be an important factor in coseismic rupture propagation and seismic phenomena in this region.

Pre-sliding Behaviour of Single Asperity Contact

The pre-sliding and static friction force behaviour at asperity level between a smooth ball and a smooth flat surface at different normal loads, as well as friction behaviour during full slip has been studied. The normal load dependence of the friction force and the preliminary displacement is discussed when the mean contact pressure is kept under 100 MPa. The theoretical model to calculate the shear stress and the preliminary displacement in the contact is discussed and the experimental data were used to verify the model. The results show that for low applied normal loads the adhesion force has an influence on the friction force measurements. Furthermore, the results for the friction force and preliminary displacement show good agreement with the theoretical trends. The experiments along with the model can be used to analyse the tangential traction in the contact and the behaviour of the stick–slip area. The measurement results along with the model were used to calculate the maximum shear stress at the point of sliding for different applied normal loads. It is also shown that at low applied normal loads the shear stress is not constant as compared to relatively high applied normal loads due to the presence of adhesion force.

Stable creeping fault segments can become destructive as a result of dynamic weakening

Faults in Earth's crust accommodate slow relative motion between tectonic plates through either similarly slow slip or fast, seismic-wave-producing rupture events perceived as earthquakes. These types of behaviour are often assumed to be separated in space and to occur on two different types of fault segment: one with stable, rate-strengthening friction and the other with rate-weakening friction that leads to stick-slip. The 2011 Tohoku-Oki earthquake with moment magnitude M(w) = 9.0 challenged such assumptions by accumulating its largest seismic slip in the area that had been assumed to be creeping. Here we propose a model in which stable, rate-strengthening behaviour at low slip rates is combined with coseismic weakening due to rapid shear heating of pore fluids, allowing unstable slip to occur in segments that can creep between events. The model parameters are based on laboratory measurements on samples from the fault of the M(w) 7.6 1999 Chi-Chi earthquake. The long-term slip behaviour of the model, which we examine using a unique numerical approach that includes all wave effects, reproduces and explains a number of both long-term and coseismic observations-some of them seemingly contradictory-about the faults at which the Tohoku-Oki and Chi-Chi earthquakes occurred, including there being more high-frequency radiation from areas of lower slip, the largest seismic slip in the Tohoku-Oki earthquake having occurred in a potentially creeping segment, the overall pattern of previous events in the area and the complexity of the Tohoku-Oki rupture. The implication that earthquake rupture may break through large portions of creeping segments, which are at present considered to be barriers, requires a re-evaluation of seismic hazard in many areas.