bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulated Strong Ground Motions for the GreatM9.3 Sumatra–Andaman Earthquake of 26 December 2004
Authors: Sørensen M. B. , Atakan K. , Pulido N.
Published: January 2007

On 26 December 2004, a devastating earthquake of M 9.3 occurred offshore northern Sumatra. Due to the size of this earthquake and the accompanying tsunami wave, disastrous consequences have been observed in several countries around the Indian Ocean. The tectonics in the region are characterized by the oblique, north-northeast-oriented subduction of the Indian–Australian plate under the Sunda microplate with a rate of 6–6.5 cm/yr. This oblique convergence results in strain partitioning, where the trench-perpendicular thrust faulting along the subducting slab accommodates the east–west component of the motion, whereas the north–south component of the motion is probably accommodated by the right-lateral strike-slip faulting along the Great Sumatran fault and the Mentawi fault. Source parameters of the 26 December 2004 event have been used for modeling the resulting ground motions in the nearby affected regions. Results give an insight on the importance of ground shaking in the total destruction of places like Banda Aceh, northern Sumatra, Indonesia. The modeling is performed for a multiasperity finite fault using a hybrid procedure combining deterministic modeling at low frequencies and semistochastic modeling at high frequencies. Results show that strong shaking was distributed over a large area including northwestern Sumatra and its offshore islands. In Banda Aceh, which experienced significant damage, bedrock velocities reached 60 cm/sec with duration of the shaking of ca. 150 sec. The largest ground motions occurred near the strongest asperities of the fault plane, where velocities of 200 cm/sec are modeled for bedrock conditions.
Coseismic Slip Distributions of the 26 December 2004 Sumatra–Andaman and 28 March 2005 Nias Earthquakes from gps Static Offsets
Authors: Banerjee Paramesh , Pollitz Fred , Nagarajan B. , Bürgmann Roland
Published: January 2007

Static offsets produced by the 26 December 2004 M ∼9 Sumatra– Andaman earthquake as measured by Global Positioning System (gps) reveal a large amount of slip along the entire ≳1300 km-long rupture. Most seismic slip inversions place little slip on the Andaman segment, whereas both near-field and far-field gps offsets demand large slip on the Andaman segment. We compile available datasets of the static offset to render a more detailed picture of the static-slip distribution. We construct geodetic offsets such that postearthquake positions of continuous gps sites are reckoned to a time 1 day after the earthquake and campaign gps sites are similarly corrected for postseismic motions. The newly revised slip distribution (Mw 9.22) reveals substantial segmentation of slip along the Andaman Islands, with the southern quarter slipping ∼15 m in unison with the adjacent Nicobar and northern Sumatran segments of length ∼700 km. We infer a small excess of geodetic moment relative to the seismic moment. A similar compilation of gps offsets from the 28 March 2005 Nias earthquake is well explained with dip slip averaging several meters (Mw = 8.66) distributed primarily at depths greater than 20 km.

Online material: Offset estimation procedure, comparison of results to other studies and simpler solutions, and tables of coseismic offsets can be found here: https://www.seismosoc.org/Publications/BSSA_html/bssa_97-1a/05609-esupp/#figS6
Numerical Modeling of the Great 2004 Indian Ocean Tsunami: Focus on the Mascarene Islands
Authors: Hébert H. , Sladen A. , Schindelé F.
Published: January 2007

On 26 December 2004, the Mw 9.2 Sumatra earthquake triggered the greatest tsunami ever observed in recent times. The unprecedented quality and variety of observations on modern instruments provide opportunities to refine modeling techniques as well as our perception of tsunami hazard in oceanic regions where historical events are not as frequent as in the Pacific Ocean. We present a numerical modeling of the 2004 tsunami on the Mascarene Islands with refined computations on La Réunion Island, where postevent survey observations and one tide gauge record are available. We use two different source models (models A and B) to account for the observations, and we also test an additional source model (model C) to study the effect of a tsunami originating in the 1833 epicentral area (southern Sumatra). A wave trapped on the edge of La Réunion may explain the greatest water heights reached in the western coastline of the island. The observed tide gauge data are reasonably well fit (models A and B). The run-up data can also be explained with our models. Late disturbances observed in La Pointe des Galets may be explained by a late tsunami reflection from Madagascar or by harbor resonances. Finally we also show that model C (1833-like) strikes La Réunion more heavily than models A and B.
Tsunami Source of the 2004 Sumatra–Andaman Earthquake Inferred from Tide Gauge and Satellite Data
Authors: Fujii Yushiro , Satake Kenji
Published: January 2007

Tsunami source of the 2004 Sumatra–Andaman earthquake was estimated from a joint inversion of tsunami waveforms recorded on tide gauges and sea surface heights captured by satellite altimetry measurements. The earthquake, the largest in the past 40 years, caused devastating tsunami damage to countries around the Indian Ocean, but the tsunami source, in particular, its northern end, was not well resolved. Although aftershocks and crustal deformation extended from off northwestern Sumatra Island through the Nicobar Islands to the Andaman Islands, some seismic-wave analyses indicated a shorter source length, several hundred kilometers. We used tsunami waveforms recorded at 12 tide gauge stations around the source and the sea surface heights measured by three satellites: Jason1, topex/Poseidon, and Envisat. We numerically computed tsunami propagation using realistic bathymetry; more than 66,000 depth points were digitized from nautical charts and combined with the ETOPO2 data. Inversion of satellite data indicates that the tsunami source extended to the Andaman Islands with a total length of 1,400 km, but such a model produces much larger tsunami waveforms than observed at Indian tide gauge stations. Inversion of tide gauge records and the joint inversion indicate that the tsunami source was about 900 km long. The largest slip, about 13 to 25 m, was located off Sumatra Island and the second largest slip, up to 7 m, near the Nicobar Islands. The slip distribution is similar for different rupture velocities and rise times, with a slow velocity of 1 km/sec and a rise time of 3 min yielding the largest variance reduction.
Teleseismic Relocation and Assessment of Seismicity (1918–2005) in the Region of the 2004Mw 9.0 Sumatra–Andaman and 2005Mw 8.6 Nias Island Great Earthquakes
Authors: Engdahl E. Robert , Villaseñor Antonio , DeShon Heather R. , Thurber Clifford H.
Published: January 2007

The Mw 9.0 2004 Sumatra–Andaman Islands and Mw 8.6 Nias Island great earthquake sequences have generated over 5000 catalog-reported earthquakes along ∼1700 km of the Sumatra–Andaman and western Sunda regions. Studies of prior regional seismicity have been limited to global catalog locations that often have poorly constrained epicenters and depths. Approximately 3650 teleseismically well- recorded earthquakes occurring in this region during the period 1918–2005 are relocated with special attention to focal depth. Reduced uncertainties of epicenters and depths in the region (on the order of 15 and 10 km, respectively) foster interpretation of focal mechanism data and provide additional details about the subducting Indian and Australian plates. The revised earthquake dataset reveals a sharp delineation between aftershocks of the 2004 and 2005 earthquakes near Simeulue Island and a steepening in slab dip from south to north. The downdip width of the aftershock zone of the 2004 Mw 9.0 earthquake varies from ∼200 km at its northern end to ∼275 km at its southern end, and events located between 35 and 70 km focal depth occur more frequently in the southernmost section of this aftershock zone. Outer- rise and near-trench normal and strike-slip faulting earthquakes also increase in frequency following the 2004 and 2005 earthquakes. Earthquake swarms triggered along the Andaman backarc spreading center both north of Sumatra and near Siberut Island, 100 km south of the Nias Island aftershock sequence, illustrate the complex and variable nature of seismicity following these great earthquakes.
Did the 2004 Sumatra–Andaman Earthquake Involve a Component of Tsunami Earthquakes?
Authors: Seno Tetsuzo , Hirata Kenji
Published: January 2007

Tsunami earthquakes are characterized by (1) slow slip and (2) tsunamis larger than expected from seismic slip. We examine whether the 2004 Sumatra– Andaman earthquake had these features and thus involved a component of tsunami earthquakes. Fitting the effective moment versus frequency curve, we obtain characteristic times τ (Kanamori, 1972) of 70 and 290 sec. The former is on the scaling for normal earthquakes; the latter is longer. In the area off northern Sumatra, by back- projecting the wavefront recorded on the sea surface height (ssh) by the satellite altimetry, we estimate the seaward edge of the fault plane to be located at the deformation front. We then invert the ssh, assuming that the seaward edge of the fault is at this location, and obtain a maximum slip of 40 m, which was estimated to be 15 m previously. This amount of slip, approximately twice the slip estimated seismologically and geodetically, suggests that additional crustal deformation, such as inelastic uplift of the trench sediments, might have occurred near the deformation front. We propose that a similar, possibly slow, slip occurred in the shallow subduction boundary, extending from all over the rupture zone derived by the body-surface waves, with a smaller northward propagation velocity, corresponding to the longer τ. This rupture mode would solve the enigmatic features of this event seen in the seismological and tsunami data. The 2004 Sumatra–Andaman earthquake, having both features (1) and (2) that characterize tsunami eathquakes, likely had a component of tsunami earthquakes.
Implications of the 26 December 2004 Sumatra–Andaman Earthquake on Tsunami Forecast and Assessment Models for Great Subduction-Zone Earthquakes
Authors: Geist Eric L. , Titov Vasily V. , Arcas Diego , Pollitz Fred F. , Bilek Susan L.
Published: January 2007

Results from different tsunami forecasting and hazard assessment models are compared with observed tsunami wave heights from the 26 December 2004 Indian Ocean tsunami. Forecast models are based on initial earthquake information and are used to estimate tsunami wave heights during propagation. An empirical forecast relationship based only on seismic moment provides a close estimate to the observed mean regional and maximum local tsunami runup heights for the 2004 Indian Ocean tsunami but underestimates mean regional tsunami heights at azimuths in line with the tsunami beaming pattern (e.g., Sri Lanka, Thailand). Standard forecast models developed from subfault discretization of earthquake rupture, in which deep- ocean sea level observations are used to constrain slip, are also tested. Forecast models of this type use tsunami time-series measurements at points in the deep ocean. As a proxy for the 2004 Indian Ocean tsunami, a transect of deep-ocean tsunami amplitudes recorded by satellite altimetry is used to constrain slip along four subfaults of the M >9 Sumatra–Andaman earthquake. This proxy model performs well in comparison to observed tsunami wave heights, travel times, and inundation patterns at Banda Aceh. Hypothetical tsunami hazard assessments models based on end- member estimates for average slip and rupture length (Mw 9.0–9.3) are compared with tsunami observations. Using average slip (low end member) and rupture length (high end member) (Mw 9.14) consistent with many seismic, geodetic, and tsunami inversions adequately estimates tsunami runup in most regions, except the extreme runup in the western Aceh province. The high slip that occurred in the southern part of the rupture zone linked to runup in this location is a larger fluctuation than expected from standard stochastic slip models. In addition, excess moment release (∼9%) deduced from geodetic studies in comparison to seismic moment estimates may generate additional tsunami energy, if the exponential time constant of slip is less than approximately 1 hr. Overall, there is significant variation in assessed runup heights caused by quantifiable uncertainty in both first-order source parameters (e.g., rupture length, slip-length scaling) and spatiotemporal complexity of earthquake rupture.
Slip of the 2004 Sumatra–Andaman Earthquake from Joint Inversion of Long-Period Global Seismic Waveforms and gps Static Offsets
Authors: Rhie Junkee , Dreger Douglas , Bürgmann Roland , Romanowicz Barbara
Published: January 2007

The 26 December 2004 Great Sumatra–Andaman earthquake opened a new era for seismologists to understand the complex source process of a great earthquake. This is the first event with moment magnitude greater than 9 since the deployment of high-dynamic-range broadband seismic and Global Positioning System (gps) sensors around the globe. This study presents an analysis of the ruptured fault- plane geometry and slip distribution using long-period teleseismic data and gps- measured static surface displacements near the fault plane. We employ a rupture geometry with six along-strike segments with and without a steeper down-dip extension. The fault segments are further subdivided into a total of 201 ∼30 × 30 km fault patches. Sensitivity tests of fault-plane geometry and the variation in rupture velocity indicate that the dip and curvature of the fault plane are not well resolved from the given data set and the rupture velocity is constrained to be between 1.8 and 2.6 km/sec. Error estimations of the slip distribution using a random selection of seismic and gps station subsets (50% of all stations) illustrate that slip is well resolved along the whole rupture and the mean slip uncertainty is less than 1.5 m (about 11%). Although it is possible that near-field gps data include contributions from additional postseismic transient deformation, our preferred model suggests that the Sumatra–Andaman earthquake had a magnitude of Mw 9.20 + 0.05/−0.06.

Online material: Comparison of slip models, gps modeling, waveform fit, fault geometry, and inversion parameters.
Constraining the Overall Kinematics of the 2004 Sumatra and the 2005 Nias Earthquakes Using the Earth’s Gravest Free Oscillations
Authors: Lambotte S. , Rivera L. , Hinderer J.
Published: January 2007

The giant Aceh–Sumatran 2004 earthquake is the largest earthquake recorded since the great Chilean 1960 and the Alaskan 1964 events. The Earth’s free oscillations were strongly excited and recorded by numerous stations with an extremely good signal-to-noise ratio, even for the gravest modes. These particular modes are interesting because phases of these well-separated split free oscillations carry information on the overall kinematics of the source of large earthquakes (Mw >8) and, in particular, on the length, duration, and mean rupture velocity. Using the singlet-stripping technique, we study some of the Earth’s gravest free oscillations (0S2, 0S3, 0S4, 1S2, 0S0, and 1S0) recorded at several broadband permanent stations (Geoscope, Incorporated Research Institutions for Seismology [iris], Global Geodynamics Project [ggp]) to recover individual singlet parameters: phases, frequencies, and quality factors. We use these parameters to constrain the spatiotemporal extent of the source of the Sumatra earthquake of 26 December 2004 and the Nias earthquake of 28 March 2005. We mainly use vertical-component data from seismometers and superconducting gravimeters, because they are less noisy than the horizontal seismic data, but we also show that, for the 2004 event, horizontal components can also be used (1S2). On the basis of the initial phase measurements presented here, we obtain, for the 2004 event, a fault length of about 1250 km and a duration of about 550 sec. For the 2005 event, our measurements favor a model in which the southern segment breaks ≈40 sec later, but the bilateral nature of the rupture and its spatial dimension prevent us from properly constraining its spatial extent.
Comparative Analysis of the Free Oscillations Generated by the Sumatra– Andaman Islands 2004 and the Chile 1960 Earthquakes
Authors: Braitenberg Carla , Zadro Maria
Published: January 2007

The Chile 1960 and Sumatra–Andaman Islands 2004 earthquakes are among the three greatest events that have occurred since the instrumental recording of seismic waves. The two events have similarities in hypocentral depth and focal mechanism but are very different when considering the extension of the fault plane. The recent event has close to 50% greater length than the Chile event, and although the moment magnitude of the Chile event is 0.2 to 0.5 points greater, the magnitude determination of the Sumatra–Andaman depends on the frequency range considered in the calculations (free oscillations with periods > 1000 sec or seismic waves, with periods of 300–500 sec). For the Chile event only the seismic moment for periods of T < 1000 sec is presently available, although the estimate of seismic moment at larger periods is crucial for a comparison of the two events. Our study makes a direct comparison of the free oscillation amplitudes of the two events by analyzing the records of the Grotta Gigante long-base tiltmeters, which have been recording tilt continuously since 1960. The particular mountings and physical dimension of the instruments make them particularly apt to record the torsional free oscillation waves, scarcely observed by standard long-period seismographs and not directly observable by the gravity meters. We determine the singlet frequencies for some of the lower spheroidal and torsional modes and a broad spectrum of multiplet frequencies for the higher modes. After correcting for the decay of the modes, we determine the amplitude ratios of the activated modes for the two events. The amplitude ratios vary between 1.5 and 3. Our results can be used directly for determining the ratios of the seismic moments of the two events over the frequency range 0.3–3 mHz, the only necessary correction being that of the site dependence of the free mode amplitudes.
Seismicity Associated with the Sumatra–Andaman Islands Earthquake of 26 December 2004
Authors: Dewey James W. , Choy George , Presgrave Bruce , Sipkin Stuart , Tarr Arthur C. , Benz Harley , Earle Paul , Wald David
Published: January 2007

The U.S. Geological Survey/National Earthquake Information Center (usgs/neic) had computed origins for 5000 earthquakes in the Sumatra–Andaman Islands region in the first 36 weeks after the Sumatra–Andaman Islands mainshock of 26 December 2004. The cataloging of earthquakes of mb (usgs) 5.1 and larger is essentially complete for the time period except for the first half-day following the 26 December mainshock, a period of about two hours following the Nias earthquake of 28 March 2005, and occasionally during the Andaman Sea swarm of 26–30 January 2005. Moderate and larger (mb ≥5.5) aftershocks are absent from most of the deep interplate thrust faults of the segments of the Sumatra–Andaman Islands subduction zone on which the 26 December mainshock occurred, which probably reflects nearly complete release of elastic strain on the seismogenic interplate-thrust during the mainshock. An exceptional thrust-fault source offshore of Banda Aceh may represent a segment of the interplate thrust that was bypassed during the mainshock. The 26 December mainshock triggered a high level of aftershock activity near the axis of the Sunda trench and the leading edge of the overthrust Burma plate. Much near-trench activity is intraplate activity within the subducting plate, but some shallow-focus, near-trench, reverse-fault earthquakes may represent an unusual seismogenic release of interplate compressional stress near the tip of the overriding plate. The interplate-thrust Nias earthquake of 28 March 2005, in contrast to the 26 December aftershock sequence, was followed by many interplate-thrust aftershocks along the length of its inferred rupture zone.
Rupture Process of the 2004 Sumatra–Andaman Earthquake from Tsunami Waveform Inversion
Authors: Piatanesi Alessio , Lorito Stefano
Published: January 2007

The aim of this work is to infer the slip distribution and rupture velocity along the rupture zone of the 26 December 2004 Sumatra–Andaman earthquake from available tide gage records of the tsunami. We selected waveforms from 14 stations, distributed along the coast of the Indian Ocean. Then we subdivided the fault plane into 16 subfaults (both along strike and downdip) following the geometry and mechanism proposed by Banerjee et al. (2005) and computed the corresponding Green’s functions by numerical solution of the shallow-water equations through a finite- difference method. The slip distribution and rupture velocity were determined simultaneously by means of a simulated annealing technique. We compared the recorded and synthetic waveforms in the time domain, using a cost function that is a trade-off between the L1 and L2 norms. Preliminary tests on a synthetic dataset, together with a posteriori statistical analysis of the model ensemble enabled us to assess the effectiveness of the method and to quantify the model uncertainty. The main finding is that the best source model features a nonuniform distribution of coseismic slip, with high slip values concentrated into three main patches: the first is located in the southern part of the fault, off the coast of the Aceh Province; the second between 6.5° N and 11° N; and the third at depth, between 11° N and 14° N. Furthermore, we estimated that the rupture propagated at an average speed of 2.0 km/sec.
Aftershock Investigation in the Andaman–Nicobar Islands of India and Its Seismotectonic Implications
Authors: Mishra O. P. , Kayal J. R. , Chakrabortty G. K. , Singh O. P. , Ghosh D.
Published: January 2007

Six three-component short-period digital seismograph (four Reftek and two Kinemetrics) stations were established in different parts of the Andaman– Nicobar Islands following the 26 December 2004 devastating Sumatra–Andaman mainshock (Mw 9.3). Here, we analyze about 18,000 aftershocks (M ≥3.0) recorded from 6 January to 16 March 2005 to better understand the seismotectonics of the region. A sudden burst of aftershock activity with irregular trend in the month of January 2005 was observed at almost all seismograph stations. The estimate of P- value = 0.9532 from aftershocks (M ≥4.5) is near to normal value of 1.0, which suggests a slow decay sequence of aftershock with complex and nonuniform stress change in a fault system (creep effects and history-dependent stress changes). The frequency–magnitude relation of the aftershocks followed the power law with average b-value of 0.7723 and it varies from 0.49 to 1.03, indicating the compressive stress state of the region and its heterogeneous structure with possible variations in frictional conditions along the fault. The distribution of the located aftershocks by a multistation method shows a north–south-trending aftershock cluster in an area of about 800 × 300 km2, which reflects an approximate rupture dimension of the mainshock beneath the Andaman–Nicobar Islands. Most of aftershocks occurred in a depth range of 5–65 km. The determination of composite fault-plane solutions of the best located aftershock clusters at three different depth ranges (0–15, 16–30, and >31 km) in the ten blocks of the region suggests that the mainshock rupture propagated through normal, reverse, and strike-slip earthquakes. The areas in the vicinity of Barren and Narcondum volcanic zones show a dominantly normal fault mechanism due to predominant tensional forces, suggesting the facilitation of brittle failure in the weakened crust by the process of underheating. The zone near Baratang mud volcano is associated predominantly with thrust fault at depth of 0–30 km, suggesting a high compressive force beneath the Baratang that ejected a huge amount of mud and slurry materials to the surface after the 26 December 2004 Sumatra–Andaman earthquake (Mw 9.3). Here, we propose that the relocation of our large aftershock dataset using converted sP-depth-phase technique for precise depth control is needed, and its sharing with global earthquake data can render more information on the subduction dynamics and geodynamical processes of the region.
Coseismic Slip and Afterslip of the GreatMw 9.15 Sumatra–Andaman Earthquake of 2004
Authors: Chlieh Mohamed , Avouac Jean-Philippe , Hjorleifsdottir Vala , Song Teh-Ru Alex , Ji Chen , Sieh Kerry , Sladen Anthony , Hebert Helene , Prawirodirdjo Linette , Bock Yehuda , Galetzka John
Published: January 2007

We determine coseismic and the first-month postseismic deformation associated with the Sumatra–Andaman earthquake of 26 December 2004 from near- field Global Positioning System (gps) surveys in northwestern Sumatra and along the Nicobar-Andaman islands, continuous and campaign gps measurements from Thailand and Malaysia, and in situ and remotely sensed observations of the vertical motion of coral reefs. The coseismic model shows that the Sunda subduction megathrust ruptured over a distance of about 1500 km and a width of less than 150 km, releasing a total moment of 6.7–7.0 × 1022 N m, equivalent to a magnitude Mw ∼9.15. The latitudinal distribution of released moment in our model has three distinct peaks at about 4° N, 7° N, and 9° N, which compares well to the latitudinal variations seen in the seismic inversion and of the analysis of radiated T waves. Our coseismic model is also consistent with interpretation of normal modes and with the amplitude of very-long-period surface waves. The tsunami predicted from this model fits relatively well the altimetric measurements made by the jason and topex satellites. Neither slow nor delayed slip is needed to explain the normal modes and the tsunami wave. The near-field geodetic data that encompass both coseismic deformation and up to 40 days of postseismic deformation require that slip must have continued on the plate interface after the 500-sec-long seismic rupture. The postseismic geodetic moment of about 2.4 × 1022 N m (Mw ∼8.8) is equal to about 30 ± 5% of the coseismic moment release. Evolution of postseismic deformation is consistent with rate-strengthening frictional afterslip.

Online material: Summary of geodetic data used in this study.
Rupture Kinematics of the 2005Mw 8.6 Nias–Simeulue Earthquake from the Joint Inversion of Seismic and Geodetic Data
Authors: Konca A. Ozgun , Hjorleifsdottir Vala , Song Teh-Ru Alex , Avouac Jean-Philippe , Helmberger Don V. , Ji Chen , Sieh Kerry , Briggs Richard , Meltzner Aron
Published: January 2007

The 2005 Mw 8.6 Nias–Simeulue earthquake was caused by rupture of a portion of the Sunda megathrust offshore northern Sumatra. This event occurred within an array of continuous Global Positioning System (gps) stations and produced measurable vertical displacement of the fringing coral reefs above the fault rupture. Thus, this earthquake provides a unique opportunity to assess the source characteristics of a megathrust event from the joint analysis of seismic data and near-field static co-seismic displacements. Based on the excitation of the normal mode data and geodetic data we put relatively tight constraints on the seismic moment and the fault dip, where the dip is determined to be 8° to 10° with corresponding moments of 1.24 × 1022 to 1.00 × 1022 N m, respectively. The geodetic constraints on slip distribution help to eliminate the trade-off between rupture velocity and slip kinematics. Source models obtained from the inversion of various combinations of the teleseismic body waves and geodetic data are evaluated by comparing predicted and observed long-period seismic waveforms (100–500 sec). Our results indicate a relatively slow average rupture velocity of 1.5 to 2.5 km/sec and long average rise time of up to 20 sec. The earthquake nucleated between two separate slip patches, one beneath Nias and the other beneath Simeulue Island. The gap between the two patches and the hypocentral location appears to be coincident with a local geological disruption of the forearc. Coseismic slip clearly tapers to zero before it reaches the trench probably because the rupture propagation was inhibited when it reached the accretionary prism. Using the models from joint inversions, we estimate the peak ground velocity on Nias Island to be about 30 cm/sec, an order of magnitude slower than for thrust events in continental areas. This study emphasizes the importance of utilizing multiple datasets in imaging seismic ruptures.
Late Mesozoic extensional tectonics in the North China block: a crustal response to subcontinental mantle removal?
Authors: Lin Wei , Wang Qingchen
Published: January 2007

In the North China block, Cretaceous extensional tectonics is expressed by numerous syntectonic plutons bounded by ductile normal faults and several metamorphic core complexes (MCC). Cretaceous half-grabens filled by continental terrigenous deposits are widespread. The examples of MCC from South Liaoning Peninsula, Yiwulüshan, Hohhot as well as the Yunmengshan syntectonic pluton spread along ca 2000 km suggest that the early Cretaceous extensional tectonics in the North China block is globally symmetric. The geodynamics setting of this continental-scale extension remains disputed. It is not satisfactorily explained by back-arc rifting related to the Paleo-Pacific subduction or crustal “unthickening”. Mantle lithosphere removal is, however, considered. Upwelling of asthenosphere may be the origin of heat advection and fluid transfer from mantle to lower crust, thus triggerring the Cretaceous magmatism, crustal softening and diffuse continental stretching. Several possible lithosphere-scale models, such as convective removal of mantle lithosphere and detachment of a large piece of mantle, are discussed.
The late extension in the inner western Alps: a synthesis along the south-Pelvoux transect
Authors: Tricart Pierre , Lardeaux Jean-Marc , Schwartz Stéphane , Sue Christian
Published: January 2007

During the Oligocene, in the central western Alps, tectonic accretion of the external domain to the internal orogenic wedge along the Briançonnais frontal thrust (BFT) was followed by backfolding, resulting in the Alpine fanning structure. The Briançonnais fan axis was rapidly exhumed by erosion. This growing wedge at the scale of the entire Alpine structure was a short-lived situation that ended with the onset of extension in its internal part, before the end Oligocene. To the east, in the Queyras Piedmont Schistes lustrés, extension in ductile then brittle conditions accommodated the tectonic denudation of the Dora-Maira crystalline massif below the Monviso ophiolites, themselves exhumed below the Queyras Schistes lustrés. Consistently, the final cooling of these Schistes lustrés becomes younger eastwards during the Miocene. To the west, inversion of the BFT was directly associated with dense normal faulting in the Briançonnais-Piedmont nappe stack. Local reactivation of thrust surfaces resulted in spectacular trains of tilted blocks oriented parallel and normal to the orogen. When considered at the scale of the entire internal zones, the brittle extension developed during the Neogene globally displays a multitrend character. It is a close to radial spreading that strongly suggests the gravitational collapse of an overthickened crust. Extensional movement along the BFT and multitrend normal faulting in its hangingwall continue at present, resulting in shallow depth seismic activity. From the Neogene onwards, the Alpine structure underwent contrasting tectonic regimes. Extension limited the growth of the internal wedge or accompanied its thinning at least in its upper part. Concurrently the external wedge continued growing through successive folding-thrusting phases.
Origin and modelling of water salinization in a coastal aquifer of the Bay of Bengal: The Kaluvelly watershed, Tamil Nadu, India
Authors: D’ozouville Noémi , Violette Sophie , Gassama Nathalie , Dia Aline , Jendrzejewski Nathalie
Published: January 2007

Over-pumping of the Vanur sandstone aquifer has led to a lowering of the piezometric surface and degradation of water quality through increased salinization. This aquifer salinization is a good example of many similar problems in India and other parts of the world. The Vanur Formation is the main aquifer of a multilayered system bordered by the sea on the eastern side and partly overlaid by the brackish waters of the Kaluvelly swamp in the north. The origin of the salinity, which apparently is not simply seawater intrusion, and its dynamics are examined, using chemical and isotopic tools together with 1D hydrological modelling of the movement of the seawater/fresh water interface.

The content of major elements and some trace elements as well as isotopic ratios (18O/16O, D/H and 87Sr/86Sr) were measured in groundwater, surface and rainwater during five sampling surveys (January 1999 to October 2001). Available data on rainfall, piezometric and hydrogeologic records were used. We identified human contamination by F, Li in parts of the aquifer, which invalidated their use as tracers.

The chemical composition of water from the Vanur aquifer shows a classical chemical evolution from the recharge area to the deeper confined area, consisting in increased water-rock interaction and a subsequent increase of solute species. However, the range of major compound concentration ratios for some wells does not follow this general trend. The non-consistent points are located in the most depressed area of the aquifer (−20 m amsl in June 2000), except in the north where the brackish water of the Kaluvelly swamps seems to enter the aquifer. In the depressed area, the sulphate signature corresponds to a mixing with a mineralized and sulphate-rich water body, likely to be Ramanathapuram sandstone water. It is due to the upward leakage from this underlying formation. A seasonal evaporation signature recorded by stable isotopes (δ18O, δD) suggests the addition of return irrigation flow. The 1D hydrodynamical model of the sea-water/fresh water movement was built with the available geological and hydraulic data. Hydrodynamic calculations show that seawater intrusion can be expected to occur within 3 to 20 years after the year 2000, depending on the value of unknown parameters (porosity) or boundary conditions (recharge, pumped volume). But we cannot rule out that a lithologic or tectonic barrier prevent any seawater intrusion inland; future geological investigation has to be done to confirm or infirm this hypothesis.
Magnolia Deepwater Development- Striving for Best-in-Class Drilling Performance
Authors: Reinhardt W. Randall , Williamson Roger N. , Eaton Luke F. , Actis Stephen C.
Published: January 2007

ConocoPhillips is developing the Magnolia field with a Tension Leg Platform (TLP) in 4,674 ft of water at Garden Banks (GB) block 783 in the Gulf of Mexico (GOM) (see Fig. 1). The field was discovered in 1999, and appraisal wells were drilled in 2000 and 2001. The well-construction strategy included drilling six additional development wells from a mobile offshore drilling unit (predrilling) before the installation of the TLP. Drilling the new wells consisted of two phases: batch-setting all six wells through 20-in. casing, followed by deepening the wells to a total depth (TD). The wells targeted multiple zones resulting in complex, designer directional wells with 50° to 60° maximum hole angles. This paper examines the application of drilling best practices used to deepen the wells to TD after batch-setting operations were complete (Eaton et al. 2005).

To minimize drilling costs while deepening the wells to TD, project goals were to eliminate trouble time; minimize combined drilling, circulating and tripping time per interval; maximize simultaneous activities; and reduce the number of trips necessary to drill the well. The goal of achieving Best-in-Class performance requires detailed planning, documenting, and implementing of results and lessons learned; effective communications; equipment quality control; and implementation of a team environment with all the companies involved in the drilling program. The complex high-angle wells require employing extended reach best practices to balance on-bottom drilling performance with the ability to effectively clean the hole to enable trouble-free tripping of the bottomhole assembly (BHA), running of casing, and obtaining primary cement jobs.

The best practices discussed in this paper include changes made to improve rotary steerable reliability; simultaneous drilling and under reaming BHA design (Eaton et al. 2001); hole cleaning; and torque and drag monitoring. The paper also discusses activities that reduced the number of required trips and activities conducted out of critical path, such as moving the subsea blowout preventor (BOP) from wellhead to wellhead with an innovative BHA, a BHA to run and retrieve wear bushings, subsea guidebase installation by way of a winch and remote operated vehicle (ROV), off-critical-path makeup of BHA components, and drillstring management.
Solid Expandable Tubular Technology: The Value of Planned Installation vs. Contingency
Authors: Carstens Chris , Strittmatter Kate
Published: January 2007

Narrow pore-pressure/fracture gradient windows often necessitate additional casing strings to maintain wellbore stability and reach deeper objective depths. Operators are constrained by the number of strings of conventional casing that can run through subsea or surface wellhead equipment. Planning solid expandable tubulars into the well design allows the operator to run additional casing strings to reach deeper objectives. Traditionally, there are two approaches used in selecting expandable tubular technology: one selects a solid expandable tubular for use as a contingency and installs it after encountering problems, often deep in a distressed well; and the other installs a large-bore expandable in the upper section of the well as part of the base well design.

Using a solid expandable tubular system in the upper sections of the well design preserves hole size from the onset and allows more casing strings to be run without pushing casing points to the fracture-gradient limit. Preserving hole size contributes to drilling efficiency, reduces equivalent circulation density (ECD), and minimizes risk associated with small-hole size in deeper sections of the wellbore.

Another application for solid expandable tubulars is in conjunction with surface blowout preventer (BOP) stack technology. Typical surface stack systems are drilled using a subsea stack BOP system coupled to a 13⅜-in. or 16-in. high-pressure drilling riser. After setting the riser, only one or two conventional casing strings can be run through the riser, which limits chances of drilling to deeper geologic objectives.

This paper looks at two case histories. The first case history compares two deepwater offset wells in the Mississippi Canyon area of the Gulf of Mexico (GoM). One well used expandable casing as a contingency late in the well execution phase, and the other well incorporated the expandable casing as part of the base design in an upper-hole section. The second case history evaluates a well in which solid expandable tubular technology allows up to three additional casing strings to be run in a surface-stack application. This paper discusses how combining solid expandable tubular technology with surface-stack technology pushes the technical limits of surface-stack drilling into deeper water and deeper formations.
Belief and the American Folk
Authors: Mullen Patrick B.
Published: January 2007

The history of folklore scholarship has come under increasing scrutiny in terms of cultural representations of the folk, but the role of folk belief in the construction of the folk has not been thoroughly examined. An investigation into American folklore scholarship of the last 100 years reveals that folk belief has been used to justify both romantic images of the folk as wise and natural and scientific rationalistic images of the folk as pathological, with complex combinations of the two extremes. More recently, reflexive ethnography and cultural politics have offered ways of escaping the restrictions of these older paradigms in folk belief studies, although problems still remain.
Fluid Subjectivities: Intertextuality and Women’s Narrative Performance in North India
Authors: Meyer Rachel S.
Published: January 2007

An investigation of intertextual gaps located in utterances offers a useful strategy for feminist interpretations of narrative performances. In order to complicate the notion of a "gendered consciousness," intertextual analysis forces encounters with the interfused, split meanings that grow in the permeable spaces of "women’s words" and enables us to confront contradiction and ambiguity involved in verbal identifications with subject positionings.
Otherness and Otherworldliness: Edward W. Lane’s Ethnographic Treatment ofThe Arabian Nights
Authors: Schacker-Mill Jennifer
Published: January 2007

In this article, I trace the conceptions of textual and national character that shaped Edward W. Lane’s early Victorian edition of the Arabian Nights. Lane sought to locate Alf Layla wa- Layla in a broad cultural and oral discursive context for a newly widened English readership. His treatment of the Nights offers vantage points on the interrelationship of ethnographic and fantasy genres and on the emergence of folkloristic and Orientalist discourses in popular publications.
The Hybrid Metaphor: From Biology to Culture
Authors: Stross Brian
Published: January 2007

This article introduces and briefly discusses a few conceptual considerations common to biological and cultural hybridity and examines the biological concept of "hybrid vigor" as it can be applied to the cultural realm of hybridity, illustrating this with a hybrid form of communication in cyberspace. The notion of a hybridity cycle is introduced, along with stages in the cycle whereby a hybrid form becomes a purebred and then parent of another hybrid.
Travel Warning: Elite Appropriations of Hybridity, Mestizaje, Antiracism, Equality, and Other Progressive-Sounding Discourses in Highland Guatemala
Authors: Hale Charles R.
Published: January 2007

This article analyzes the complexities that arise when certain keywords in culture theory "travel" from one sociopolitical setting to another. The specific context is ethnic and racial relations in the highlands of Guatemala, where members of the dominant (ladino) group have come to use the term hybridity (among others) to challenge and delegitimate Maya Indians’ demands for cultural rights. I conclude with a call for theory-making efforts without pretensions of universal resonance, grounded instead in an active engagement with the politics of a particular place, time, and people.
Conjuring in the Big House Kitchen: An Interpretation of African American Belief Systems Based on the Uses of Archaeology and Folklore Sources
Authors: Leone Mark P. , Fry Gladys-Marie
Published: January 2007

Joining archaeological and folkloristic methods, the authors compare the archaeological remains of African religious practices found in Virginia sites from the 18th and 19th centuries with historical data on conjuring and divining. The contents of diviners’ bundles buried beneath hearths and sills and in northeast corners are presented from Virginia sites occupied by enslaved Africans and free African Americans. Those bundles are contextualized using data from narratives of former slaves and the ideas of West African religion.
Fantasía and Disobedient Daughters: Undistressing Genres and Reinventing Traditions in the Mexican American Carpa
Authors: Haney Peter C.
Published: January 2007

During the 1930s and 1940s, female performers in Mexican American tent shows in San Antonio modified the costumes associated with Mexican "folkloric" dances, incorporating elements derived from vaudeville, to form a hybrid style called fantasía. This style asserted Mexican American identity while subverting the purist nationalism of folklórico dances and marking the performers’ entry into newly public female roles. At the same time, it also involved the performers in reified masculinist discourses of female beauty and fashion.
". . . Hidden Right out in the Open": The Field of Folklore and the Problem of Invisibility 1998 American Folklore Society Presidential Address
Authors: Roberts John W.
Published: January 2007

This address represents an attempt to sketch a history of academic folklore in the United States as a way of understanding the difficulties that the field has experienced in achieving and sustaining an identity as an independent discipline in colleges and universities. In developing its argument, the essay draws an analogy between folklore’s struggle to achieve individual disciplinary status and the struggle for individual identity by the protagonist in Ralph Ellison’s novel Invisible Man. For both folklore and Ellison’s protagonist, membership in communities historically perceived in stereotypical terms becomes viewed as "the problem" in achieving individuality rather than a source of identity. Therefore, folklore’s "identity problem" is examined in terms of both external and internal factors that have influenced it over time. By understanding this history, one is better able to understand what many currently perceive as an institutional crisis surrounding some folklore departments and programs.
African Folk and the Challenges of a Global Lore: 1998 American Folklore Society Plenary Address
Authors: Yankah Kwesi
Published: January 2007

The politics of knowledge production and dissemination unfairly subsumes local intellectual paradigms under received Western hegemonies, thereby shifting the power base of knowledge. This trend contributes in obscuring Africa’s contribution to the study of folklore. This essay advocates a revision of the world academic order toward a greater formalization of local knowledge.
The Self in "Fieldwork": A Methodological Concern
Authors: Stoeltje Beverly J. , Fox Christie L. , Olbrys Stephen
Published: January 2007

As concepts of reflexivity and postcolonial perspectives have advanced our understandings of the way we represent those we study, they have also introduced a consciousness of the role of the self in research. This article reviews the history of the field of folklore with regard to the method of obtaining data or texts and demonstrates that collecting material contrasts with the practice of conducting research in the field. Pointing to a moment of transition, it shows that theories of folklore had to undergo significant change before methods of research would acknowledge the identity of the fieldworker and its significance.
The Aesthetics of Play in Reunified Germany’s Carnival
Authors: McMahon Felicia Faye
Published: January 2007

On 11 November, two days after the fall of the Berlin Wall, carnival enthusiasts in Chemnitz celebrated by dressing in nightgowns and running through the streets as they openly mocked the old regime. In play forms such as carnival, both sense and nonsense exist side by side, but not infrequently the latter disintegrates into disorder, with no reference to any context outside of itself. Such a condition is possible because of the paradoxical nature of play, and I here suggest that nonsense in and of itself should be considered the essential element of "carnival aesthetics." However, when other influences such as politics override the carnival, this playfulness is essentially lost, and the festival becomes ideological display as evidenced by the history of the German carnival known as "Fasching."