Slip Area Research Articles

Postseismic response of repeating earthquakes around the 2011 Tohoku‐oki earthquake: Moment increases due to the fast loading rate

AbstractWe examined the temporal variation of the size of repeating earthquakes related to the 2011 Tohoku‐oki earthquake (M9.0) in the northeastern Japan subduction zone for the period from July 1984 to the end of 2011. The repeaters (M2.5–6.1) show postseismic magnitude increases for most sequences located in the area of large postseismic slip at the downdip extension of the M9 source region. The magnitudes of the first events after the M9 earthquake increased by an average of about 0.3 for sequences having three or more earthquakes over the 9 months following it. We also examined the slip area in detail for Kamaishi repeaters whose magnitudes had been M4.9 ± 0.2 but which increased by about 1 after the M9 earthquake. Waveform modeling shows that the slip area for the post‐M9 Kamaishi earthquakes overlaps with that before the Tohoku‐oki earthquake but enlarged by about 6 times. Until the occurrence time of the last event (September 2011) in the analysis period, the rupture area remained larger than before but appeared to shrink over time. The enlargement of the rupture area suggests that an aseismic‐to‐seismic transition occurred in the region surrounding the pre‐M9 repeaters and is most likely related to fast loading of the repeaters due to rapid postseismic slip estimated to have occurred in the area. The existence of conditionally stable regions around the repeating earthquakes and/or patches slightly larger than the earthquake nucleation sizes may explain such behavior. The temporal change of loading rate is an important factor in determining earthquake size in this case.

Dual megathrust slip behaviors of the 2014 Iquique earthquake sequence

The transition between seismic rupture and aseismic creep is of central interest to better understand the mechanics of subduction processes. A Mw 8.2 earthquake occurred on April 1st, 2014 in the Iquique seismic gap of northern Chile. This event was preceded by a long foreshock sequence including a 2-week-long migration of seismicity initiated by a Mw 6.7 earthquake. Repeating earthquakes were found among the foreshock sequence that migrated towards the mainshock hypocenter, suggesting a large-scale slow-slip event on the megathrust preceding the mainshock. The variations of the recurrence times of the repeating earthquakes highlight the diverse seismic and aseismic slip behaviors on different megathrust segments. The repeaters that were active only before the mainshock recurred more often and were distributed in areas of substantial coseismic slip, while repeaters that occurred both before and after the mainshock were in the area complementary to the mainshock rupture. The spatiotemporal distribution of the repeating earthquakes illustrates the essential role of propagating aseismic slip leading up to the mainshock and illuminates the distribution of postseismic afterslip. Various finite fault models indicate that the largest coseismic slip generally occurred down-dip from the foreshock activity and the mainshock hypocenter. Source imaging by teleseismic back-projection indicates an initial down-dip propagation stage followed by a rupture-expansion stage. In the first stage, the finite fault models show an emergent onset of moment rate at low frequency (<0.1 Hz), while back-projection shows a steady increase of high frequency power (>0.5 Hz). This indicates frequency-dependent manifestations of seismic radiation in the low-stress foreshock region. In the second stage, the rupture expands in rich bursts along the rim of a semi-elliptical region with episodes of re-ruptures, suggesting delayed failure of asperities. The high-frequency rupture remains within an area of local high trench-parallel gravity anomaly (TPGA), suggesting the presence of subducting seamounts that promote high-frequency generation. Our results highlight the complexity of the interactions between large-scale aseismic slow-slip and dynamic ruptures of megathrust earthquakes.

Changes in the stress field after the 2008 M7.2 Iwate‐Miyagi Nairiku earthquake in northeastern Japan

AbstractIn order to investigate changes in the stress field following the 2008 M7.2 Iwate‐Miyagi Nairiku earthquake in NE Japan, we determined many focal mechanisms within the focal area, using data from both the dense aftershock observation network deployed just after the main shock and other temporary and routinely operated stations in the surrounding area. Applying stress tensor inversions to these focal mechanism data, we estimated the detailed spatial distribution of the principal stress orientations in this event's source area. Estimated orientations of the maximum principal stress (σ1) axes differ significantly before and after the main shock. Before the main shock, the σ1 axis is oriented WNW‐ESE across the entire studied area, which is parallel to the plate convergence direction. After the main shock, however, the orientation of the σ1 axis changed significantly and showed remarkable spatial variation. In the northern and southern parts of the aftershock area, located relatively far from the main shock large slip area, the σ1 axes are oriented WNW‐ESE, similar to those before the main shock. In contrast, to the east and west of the central part of the aftershock area, the σ1 axes are oriented N‐S and NE‐SW, respectively. This characteristic spatial pattern of σ1 axis orientations is approximately consistent with that of static stress change associated with the main shock rupture, which strongly suggests that the spatially heterogeneous stress after the main shock is caused by such static stress change. The differential stress magnitude before the main shock is estimated to be less than 10–30 MPa, suggesting that the main shock faults are weak.

VLIV ZATÍŽENÍ HNACÍCH NÁPRAV A VÝŠKY ZÁVĚSU NA TAHOVÉ VLASTNOSTI TRAKTORU

The goal of the experimental measurement was determination of relation among weight load of the tractor together, hitch height changes and drawbar characteristic. The measurement was realized on chassis dynamometer at MUAF in Brno. The first step consisted of rated speed characteristics measurement in conformity with OECD demands. The drawbar characteristic was measured under two selected gears. Adding 980 kg to the nominal wight of the tractor brought increasing maximal drawbar power and drawbar force together with decreasing of slip. The highest differences were observed during the mesurement of fifth gear shifted. The drawbar force grew up to 18.9% as well as the maximal drawbar power (15.2%). The maximal drawbar power at ninth gear gave 62.8 kW. The hitch height was setting to 0.54 m; 0.64 m and 0.74 m. When the hitch height was set from 0.54 m to 0.74 m the drawbar force an power on front axle was lower by reason of load reduction. As can be noticed from the final drawbar characteristics, both curves are identical up to border of maximal drawbar power. Small differences in the area of the highest slips can be ascribed to the rolling resistance.

Teleseismic inversion of the 2004 Sumatra-Andaman earthquake rupture process using complete Green’s functions

Spatial and temporal variations in coseismic slip distribution are often obtained by rupture process analyses using teleseismic body waves. Many analyses using teleseismic body waves were based on the ray theory because of the very efficiently computable direct P-, S-, and major reflected waves near the source. The 2004 Sumatra-Andaman earthquake was one of the largest earthquakes recorded in history, and the data that are required for the entire rupture process analysis include later phases such as PP waves and a very long period phase called a W phase. However, calculating these later phases using the conventional ray theoretical method is difficult. Here we investigate the rupture process of the 2004 Sumatra-Andaman earthquake using complete Green’s functions, including all later phases such as PP waves and W phase. We use the direct solution method, which computes complete synthetic seismograms up to 2 Hz for transversely isotropic spherically symmetric media, to calculate the Green’s functions. The obtained synthetic seismograms generated fit the observed seismograms quite well from a short period to a long period. The estimated slip distribution consists of four large slip areas: the largest slip occurred in the shallow part off the Sumatra west coast with a maximum slip of approximately 29 m, the second and third largest slips occurred in the shallow and deep parts of the Nicobar region with maximum slips of approximately 8 m and 7 m, respectively, and the fourth slip occurred in the middle Andaman region with a maximum slip of approximately 6 m. The estimated average rupture velocity is 2.8 km/s, but the rupture may have slowed between the Sumatra and the shallow Nicobar slip areas, and between the Nicobar and the middle Andaman slip areas. The delayed initiation of the shallow slips in the Nicobar region may possibly have been triggered by the deeper slip in the Nicobar region. There were no distinct depth-varying properties for the shallow and deep slips in the Nicobar region, as were reported for the 2011 Tohoku-Oki and 2010 Chile earthquake.

The effect of slip distribution on flow past a circular cylinder

A slip boundary has been shown to have a significant impact on flow past bluff bodies. In this work and using a circular cylinder as a model system, the effects of various slip configurations on the passing flow are investigated. A theoretical analysis using matched-asymptotic expansion is first performed in the small-Reynolds number regime following Stokes and Oseen. A slip boundary condition is shown to lead to only higher-order effects (~1/ln(Re)) on the resulting drag coefficient. For higher Reynolds numbers (100–500), the effects of five types of symmetric slip boundary conditions, namely, no slip, fore-side slip, aft-side slip, flank slip, and all slip on the flow field and pertinent parameters are investigated with numerical simulations. Detailed results on the flow structure and force distribution are presented. Flank slip is found to have the best effect for drag reduction with comparable coverage of slip area. For asymmetric slip distributions, torque and lift are found to generally occur.

AFM and SEM-FEG study on fundamental mechanisms leading to fatigue crack initiation

Early stages of surface relief evolution of persistent slip markings (PSMs) in polycrystalline 316L austenitic stainless steel cycled with constant plastic strain amplitude at 93, 173 and 573K were studied using atomic force microscopy (AFM) and high-resolution scanning electron microscopy (SEM-FEG). Qualitative and quantitative data on the morphology of PSMs, occurrence of extrusions and intrusions and the kinetics of extrusion growth are reported for all temperatures. PSMs start in all cases as surface extrusions which are later accompanied by formation of intrusions. This finding is discussed with respect to the point defect formation within areas of localized cyclic slip and primarily to their mobility at different temperatures. Consequences of migration of respective point defects for surface relief formation and the conditions for creation of fatigue crack embryos, i.e. sharp intrusions are highlighted.

Comparison of postseismic afterslip models with aftershock seismicity for three subduction-zone earthquakes: Nias 2005, Maule 2010 and Tohoku 2011

We focus on the relation between seismic and total postseismic afterslip following the Maule Mw 8.8 earthquake on 2010 February 27 in central Chile. First, we calculate the cumulative slip released by aftershock seismicity. We do this by summing up the aftershock regions and slip estimated from scaling relations. Comparing the cumulative seismic slip with afterslip models we show that seismic slip of individual aftershocks exceeds locally the inverted afterslip model from geodetic constraints. As the afterslip model implicitly contains the displacements from the aftershocks, this reflects the tendency of afterslip models to smear out the actual slip pattern. However, it also suggests that locally slip for a number of the larger aftershocks exceeds the aseismic slip in spite of the fact that the total equivalent moment of the afterslip exceeds the cumulative moment of aftershocks by a large factor. This effect, seen weakly for the Maule 2010 and also for the Tohoku 2011 earthquake, can be explained by taking into account the uncertainties of the seismicity and afterslip models. In spite of uncertainties, the hypocentral region of the Nias 2005 earthquake is suggested to release a large fraction of moment almost purely seismically. Therefore, these aftershocks are not driven solely by the afterslip but instead their slip areas have probably been stressed by interseismic loading and the mainshock rupture. In a second step, we divide the megathrust of the Maule 2010 rupture into discrete cells and count the number of aftershocks that occur within 50 km of the centre of each cell as a function of time. We then compare this number to a time-dependent afterslip model by defining the ‘afterslip to aftershock ratio’ (ASAR) for each cell as the slope of the best fitting line when the afterslip at time t is plotted against aftershock count. Although we find a linear relation between afterslip and aftershocks for most cells, there is significant variability in ASAR in both the downdip and along-strike directions of the megathrust. We compare the spatial distribution of ASAR with the spatial distribution of seismic coupling, coseismic slip and Bouguer gravity anomaly, and in each case we find no significant correlation.

Stress drop variations among small earthquakes before the 2011 Tohoku‐oki, Japan, earthquake and implications for the main shock

AbstractIt is important to assess the likely rupture characteristics of future megathrust earthquakes. One approach is to study the spatiotemporal variation of geophysical properties in active subduction zones. We explore this idea by examining stress drops of 1563 small earthquakes (Mw 3.0–4.5) shallower than 80 km in the Tohoku‐oki region before the 2011 Tohoku‐oki earthquake. Although individual stress drop estimates exhibit considerable scatter, we find a strong increase in stress drop with depth between 30 km and 60 km, whereas stress drops for shallower and deeper events, respectively, are nearly constant. We also identify lateral variations in stress drop along strike. Higher‐than‐average stress drops are found in East Aomori‐oki and Miyagi‐oki, whereas Sanriku‐oki is a moderate stress drop area. The high stress drop zone in Miyagi‐oki is located just south of the large slip area of the 2011 Tohoku‐oki earthquake, and possibly acted as a barrier to further rupture propagation during the event. In addition, the frequency dependence of the seismic radiation observed during the main shock, with proportionally higher frequencies coming from the deeper parts of the fault, mimics the depth dependence we see in small earthquakes in the same region. These results imply that smaller pre‐main shock earthquakes can provide insight into the fault properties and consequent rupture processes of future megathrust earthquakes.

Shear-wave velocity structure of the Chilean subduction zone (39–40°S) based on Rayleigh wave dispersion: evidence of fluid release and melts in the mantle beneath the Villarrica volcano

Abstract A seismic network operated from December 2008 to November 2009 in south-central Chile covering the Chile subduction zone from c. 39°S to 40°S. This segment of the subduction zone includes the highly active Villarrica volcano and the maximum slip area of the 1960 M w 9.5 earthquake. We applied surface wave dispersion analysis to data from a linear array of broadband stations and to records of four areal sub-arrays. Fifty regional and teleseismic events were used to produce dispersion curves of Rayleigh waves. From the dispersion curves, we determined depth functions of the shear-wave velocity for 4 subregions of the subduction zone: the Coastal Range, the Central Valley, the Volcanic Arc and the Back-arc Region in Argentina. The resulting models reveal the structure of the crust and the depth of the Moho discontinuity. Below the volcanic arc, the shear-wave velocities of the continental mantle are reduced by c. 7% with respect to a background value of 4.3 km s −1 . This low-velocity zone coincides with a zone of reduced electrical resistivity that was previously determined from magnetotelluric measurements. The combined occurrences of minima in the S-wave velocity and resistivity can be interpreted as an indicator of partial melts.

Computation of the effective slip of rough hydrophobic surfaces via homogenization

We present a quantitative analysis of the effect of rough hydrophobic surfaces on viscous Newtonian flows. We use a model introduced by Ybert and coauthors in [Achieving large with superhydrophobic surfaces: Scaling laws for generic geometries, Phys. Fluids 19 (2007) 123601], in which the rough surface is replaced by a flat plane with alternating small areas of slip and no-slip. We investigate the averaged slip generated at the boundary, depending on the ratio between these areas. This problem reduces to the homogenization of a nonlocal system, involving the Dirichlet to Neumann map of the Stokes operator, in a domain with small holes. Pondering on the works of Allaire [Homogenization of the Navier–Stokes equations in open sets perforated with tiny holes. I. Abstract framework, a volume distribution of holes, Arch. Rational Mech. Anal. 113 (1990) 209–259; Homogenization of the Navier–Stokes equations in open sets perforated with tiny holes. II. Noncritical sizes of the holes for a volume distribution and a surface distribution of holes, Arch. Rational Mech. Anal. 113 (1990) 261–298]. We compute accurate scaling laws of the averaged slip for various types of roughness (riblets, patches). Numerical computations complete and confirm the analysis.

A three-dimensional finite element solution of frictional wheel–rail rolling contact in elasto-plasticity

Wear, rolling contact fatigue, and plastic deformation are the major failure modes of railway wheels and rails. Proper analyses of the failure mechanisms as well as improvement in design and maintenance require an accurate evaluation of the stress and strain states. Solution of frictional rolling contact between wheel and rail in elasto-plasticity seems, however, still to lack in the literature. This paper presents a model for such a solution. A 3D finite element model is built up to simulate the rolling contact. The focus is on the tangential problem, namely the distributions of surface shear stress and micro-slip as well as the distinction of areas of adhesion and slip in the contact patch. With the presented model the assumptions of half space, linear elasticity and quasi-static or steady state, which are often employed in existing solution of rolling contact, are dropped. A bilinear elasto-plastic material with isotropic hardening is employed to examine the effects of plasticity on frictional rolling. It is found that when plastic flow occurs, the contact patch in the rail top changes from an ellipse into an egg shape; the cross influence between the normal and tangential contact problems become stronger: the normal solution is not independent of the tangential solution any more, and the tangential solution is greatly affected by the normal solution. The model can be applied to investigation of the relationships between material properties, plastic deformation, frictional work, wear, and crack initiation. Such relationships may help in better understanding the occurrence of corrugation, head checks, and squats, and may further be used for design of fatigue resistant materials and profiles of wheel and rail.

Geomagnetic storms, super‐storms, and their impacts on GPS‐based navigation systems

AbstractUsing data of GPS receivers located worldwide, we analyze the quality of GPS performance during four geomagnetic storms of different intensity: two super‐storms and two intense storms. We show that during super‐storms the density of GPS Losses‐of‐Lock (LoL) increases up to 0.25% at L1 frequency and up to 3% at L2 frequency, and up to 0.15% (at L1) and 1% (at L2) during less intense storms. Also, depending on the intensity of the storm time ionospheric disturbances, the total number of total electron content (TEC) slips can exceed from 4 to 40 times the quiet time level. Both GPS LoL and TEC slips occur during abrupt changes of SYM‐H index of geomagnetic activity, i.e., during the main phase of geomagnetic storms and during development of ionospheric storms. The main contribution in the total number of GPS LoL was found to be done by GPS sites located at low and high latitudes, whereas the area of numerous TEC slips seemed to mostly correspond to the boundary of the auroral oval, i.e., region with intensive ionospheric irregularities. Our global maps of TEC slips show where the regions with intense irregularities of electron density occur during geomagnetic storms and will let us in future predict appearance of GPS errors for geomagnetically disturbed conditions.

Finite‐fault slip model of the 2011 Mw5.6 Prague, Oklahoma earthquake from regional waveforms

AbstractThe slip model for the 2011 Mw5.6 Prague, Oklahoma, earthquake is inferred using a linear least squares methodology. Waveforms of six aftershocks recorded at 21 regional stations are used as empirical Green's functions (EGFs). The solution indicates two large slip patches: one located around the hypocenter with a depth range of 3–5.5 km; the other located to the southwest of the epicenter with a depth range from 7.5 to 9.5 km. The total moment of the solution is estimated at 3.37 × 1024 dyne cm (Mw5.65). The peak slip and average stress drop for the source at the hypocenter are 70 cm and 90 bars, respectively, approximately one half the values for the Mw5.8 2011 Mineral, Virginia, earthquake. The stress drop averaged over all areas of slip is 16 bars. The relatively low peak slip and stress drop may indicate an induced component in the origin of the Prague earthquake from deep fluid injection.

Pore pressure distribution in the focal region of the 2008 M7.2 Iwate-Miyagi Nairiku earthquake

The pore fluid pressure distribution in the focal region of the 2008 Iwate-Miyagi Nairiku earthquake was investigated through an analysis of the diversity of focal mechanisms. We inverted stress orientations and focal mechanisms directly from P-wave polarity data obtained from a dense aftershock observation network and other temporarily and routinely operated stations. The estimated stress orientation is consistent with that typical of NE Japan. Specifically, the σ 1 axis is oriented WNW-ESE nearly parallel to plate convergence, and the σ 3 axis is nearly vertical, consistent with a reverse-faulting stress regime, with some exceptions in the central part of the aftershock area. We obtained 2,497 well-determined focal mechanisms whose average number of P-wave polarity data is more than 70. The spatial distribution of pore fluid pressure was estimated by using the obtained orientations of the principal stresses and earthquake faults. The pore pressure ratio for each earthquake fault was calculated under the assumption that reduced frictional strength was caused by pore fluid pressure. The results showed that the diversity of the focal mechanisms here obtained requires high pore fluid pressures at many of the earthquake faults in the focal region. The spatial pattern of pore pressure ratio shows that areas of higher pore pressure ratio are distributed around the large coseismic slip area near Kurikoma volcano. Immediately beneath these high pore pressure areas, there exists a distinct seismic low-velocity zone that continues down to the mantle wedge below. These observations suggest that crustal fluids supplied from the mantle wedge have contributed to producing high pore pressures and to lowering the frictional strengths of those faults. Crustal fluids may also have contributed to generating the mainshock rupture.

Spatial and Temporal Variations of Aftershock Activity of the 23 October 2011 Mw 7.1 Van, Turkey, Earthquake

Abstract On 23 October 2011, an M w 7.1 earthquake struck the Van Lake region of eastern Turkey; causing vast damage in the cities of Van and Ercis. The mainshock was followed by a large number of aftershocks, which define a 60–70 km long and 30–35 km wide northeast–southwest‐trending structure, in agreement with the source rupture models derived for the main event. In this paper, we take advantage of this large data set to examine the spatial and temporal properties of the Van earthquake aftershock activity. We derive the spatial distribution of b ‐value of the Gutenberg–Richter law, as well as complementary seismicity parameters, along the surface projection of the fault plane. Recent studies have been published on the same issue, presenting controversial and sometimes opposite results. With respect to previous studies, we rely on a possibly higher quality catalog of relocated earthquakes. Furthermore, we adopt a more conservative approach, excluding from the analysis the first few days of data, until the M c reaches a stable completeness threshold; finally, we conduct statistical tests in order to check the significance of the spatial and temporal variation of b ‐value across the fault plane. Calculations are made for the complete catalog and for two independent aftershock subcatalogs, after which a stable magnitude of completeness M c is reached. For each catalog, we correlate the observed b ‐value patterns with slip distribution models of the mainshock obtained through the inversion of seismological and geodetic data. Overall, the b ‐values vary from 0.9 to 1.5 along the Van rupture fault zone. The higher b ‐values (>1.1) are observed around the epicenter of the mainshock characterizing the higher coseismic slip area on the fault projection. Low b ‐values are concentrated at the peripheral portion of the fault, away from high‐slip patches. Moreover, the b ‐value distribution over the fault plane undergoes significant variation throughout the aftershock sequence.

Observed change in plate coupling close to the rupture initiation area before the occurrence of the 2011 Tohoku earthquake: Implications from an earthquake cycle model

Changes in plate coupling off the coast of Fukushima have been detected by GPS since 2000. These changes occurred close to the rupture initiation area of the Mw9.0 2011 Tohoku earthquake and possibly initiated the earthquake. We investigated these changes with quasi-dynamic earthquake cycle simulations using a hierarchical asperity model. We modeled the entire rupture region as rate weakening but conditionally stable, while areas with huge slips and Mw7 asperities were modeled as strong and ordinary rate-weakening unstable friction, respectively. The following observed characteristics were reproduced: long recurrence time, large rupture region (including a localized huge coseismic slip area and source area of recurring Mw7 earthquakes), and a Mw7 foreshock triggering the Tohoku earthquake. Off Fukushima, repeated aseismic slips propagating northward appeared in the last half of the cycle and possibly caused the decrease in plate coupling. However, it is not necessarily related to the immediate occurrence of the giant earthquake.

Seismic and geodetic evidence for grounding‐line control of Whillans Ice Stream stick‐slip events

AbstractThe tidally modulated, stick‐slip events of Whillans Ice Stream in West Antarctica produce seismic energy from three locations near the grounding line. Using ice velocity records obtained by combining time series from colocated broadband seismometers and GPS receivers installed on the ice stream during the 2010–2011 and 2011–2012 austral summers, along with far‐field seismic recordings of elastic waves, we locate regions of high rupture velocity and stress drop. These regions, which are analogous to “asperities” in traditional seismic fault studies, are areas of elevated friction at the base of the ice stream. Slip events consistently initiate at one of two locations: near the center of the ice stream, where events associated with the Ross Sea high tide originate, or a grounding‐line spot, where events associated with the Ross Sea low tide initiate, as well as occasional high‐tide events following a skipped low‐tide event. The grounding‐line site, but not the central site, produces Rayleigh waves observable up to 1000 km away, through fast expansion of the slip area. Grounding‐line initiation events also show strong directivity in the downstream direction, indicating initial rupture propagation at 1.5 km/s, compared to an average of 0.150 km/s for the entire slip event. Following slip initiation, additional seismic energy is produced from two sources located near the grounding line: first at the downstream end of Subglacial Lake Engelhardt and second toward the farthest downstream extent of the ice stream. This evidence suggests that the stronger, higher‐friction material along the grounding line controls motion throughout the stick‐slip region.

Structural heterogeneities around the megathrust zone of the 2011 Tohoku earthquake from tomographic inversion of onshore and offshore seismic observations

We performed a three-dimensional seismic tomography around the coseismic slip area of the 2011 Tohoku earthquake. By combining data from the aftershock period collected by ocean bottom seismographs (OBSs), OBS data from previous studies off the Miyagi coast, and land seismic data, we modeled the detailed seismic velocity structure along the plate boundary from the Japan Trench to near the coastline. Our results indicate that VP, VS, and VP/VS along the plate boundary change drastically about 60 km landward from the trench axis. Trenchward of this boundary, velocities are consistent with a fluid-rich environment (low VP and VS and high VP/VS) associated with the occurrence of sediment compaction and opal-to-quartz metamorphism. This area also corresponds to the contact between the slab and upper crust or between the slab and the sediment layer. A comparison of our results with numerical simulations and geological studies suggests that thermal pressurization might have occurred near the trench axis during the 2011 Tohoku earthquake. To the west of this boundary, where VP, VS, and VP/VS have moderate values, our model showed small-scale heterogeneous structures in the subducted oceanic crust near the hypocenter of the Tohoku earthquake with regions of low and high VP/VS on the updip and downdip sides of the hypocenter, respectively. We interpret the former as corresponding to the strong coupling patch and the latter as the localized fluid-rich zone. Small-scale heterogeneities thus may affect the nucleation and rupture processes of large earthquakes.

21402 自動車の車輪横滑りを伴うダイナミック挙動のモデリングと制御に関する研究

The purpose of this study is modeling and control of the vehicle motion with wheel side slip, which is generally difficult to control. The vehicle motion is governed friction force largely generated by each tire. The friction force varies depending on the amount of slip between tire and road surface. The motion control of the vehicle has been studied in the small area of the tire slip. However, in motor racing, such as rally, drifting with large side slip which is in the nonlinear region of the tire friction force is often used when turning. By operating steering, accelerator, and brake skillfully, the driver stabilizes unstable behavior of the vehicle and runs the course as wanted. Therefore, it is considered that control of the motion with the large side slip such as the drifting becomes possible, it is useful in terms of a new motion control of the vehicle.