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1.
Flexure of the Indian plate and intraplate earthquakes 总被引：2，自引：0，他引：2
The flexural bulge in central India resulting from India's collision with Tibet has a wavelength of approximately 670 km.
It is manifest topographically and in the free-air gravity anomaly and the geoid. Calculations of the stress distribution
within a flexed Indian plate reveal spatial variations throughout the depth of the plate and also a function of distance from
the Himalaya. The wavelength (and therefore local gradient) of stress variation is a function of the effective elastic thickness
of the plate, estimates of which have been proposed to lie in the range 40–120 km. The imposition of this stress field on
the northward moving Indian plate appears fundamental to explaining the current distribution of intraplate earthquakes and
their mechanisms. The current study highlights an outer trough south of the flexural bulge in central India where surface
stresses are double the contiguous compressional stresses to the north and south. The Bhuj, Latur and Koyna earthquakes and
numerous other recent reverse faulting events occurred in this compressional setting. The N/S spatial gradient of stress exceeds
2 bars/km near the flexural bulge. The overall flexural stress distribution provides a physical basis for earthquake hazard
mapping and suggests that areas of central India where no historic earthquakes are recorded may yet be the locus of future
damaging events. 相似文献
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The seismic future of cities 总被引：1，自引：0，他引：1
Roger Bilham 《Bulletin of Earthquake Engineering》2009,7(4):839-887
The final projected doubling in Earth’s population in the next half century, requires an additional 1 billion housing units,
more dwellings constructed in a single generation than at any time in Earth’s history. Earth’s tenfold increase in population
has occurred during a time that is short compared to the return time of damaging earthquakes. In the next century, therefore,
earthquakes that had little impact on villages and towns, will be shaking urban agglomerations housing upwards of 12 million
people. An epicentral hit on a megacity has the potential to cause 1 million fatalities. The incorporation of earthquake resistant
structures in the current global building boom, despite successes in the developed nations, has been neglected in the developing
nations where historically earthquake damage has been high. The reasons for this neglect are attributed to indifference, ignorance
and corrupt practices, not due to an absence of engineering competence. Never has a generation of earthquake engineers been
faced with such a grave responsibility to exercise their skills, both political and technical, as now.
The eye is bewildered by “a city become an heap”. Robert Mallet (1862).相似文献
5.
G. R. Foulger G. Beutler Roger Bilham Pall Einarsson S. Fankhauser W. Gurtner U. Hugentobler W. Jason Morgan M. Rothacher Gunnar Thorbergsson U. Wild 《Journal of Geodesy》1993,67(3):148-172
Summary The 1986 GPS survey of Iceland aimed to: (1) establish geodetic control in the South Iceland Seismic Zone (SISZ), to study destructive earthquakes there, (2) measure a country-wide network to form the basis of a new first order national network. 51 points were surveyed, with 20–30 km spacings within the SISZ and 100 km spacings elsewhere. The data were processed using the Bernese GPS software Version 3. Analysis was difficult due to poor satellite geometry and short-period ionospheric variations. However, an ambiguity-fixed, ionosphere-free solution gave accuracies of 1–2 cm in the horizontal and 2–3 cm in the vertical for the SISZ network and an ambiguity-free, ionosphere-free solution yielded accuracies of about 5 cm for the country-wide network. An ionosphere-free solution for the total survey with ambiguities fixed for the SISZ network only gave marginal additional improvements over the two separate solutions. GPS surveying has continued annually in Iceland with measurements in South Iceland in 1989 and 1992 (Hackman 1991; Sigmundsson 1992) and in North Iceland in 1987, 1990 and 1992 (Jahn et al. 1992; Foulger et al. 1992). 相似文献
6.
Susan E Hough Stacey Martin Roger Bilham Gail M Atkinson 《Journal of Earth System Science》2003,112(3):353-373
We compiled available news and internet accounts of damage and other effects from the 26th January, 2001, Bhuj earthquake,
and interpreted them to obtain modified Mercalli intensities at over 200 locations throughout the Indian subcontinent. These
values are used to map the intensity distribution using a simple mathematical interpolation method. The maps reveal several
interesting features. Within the Kachchh region, the most heavily damaged villages are concentrated towards the western edge
of the inferred fault, consistent with western directivity. Significant sedimentinduced amplification is also suggested at
a number of locations around the Gulf of Kachchh to the south of the epicenter. Away from the Kachchh region intensities were
clearly amplified significantly in areas that are along rivers, within deltas, or on coastal alluvium such as mud flats and
salt pans. In addition we use fault rupture parameters inferred from teleseismic data to predict shaking intensity at distances
of 0–1000 km. We then convert the predicted hard rock ground motion parameters to MMI using a relationship (derived from internet-based
intensity surveys) that assigns MMI based on the average effects in a region. The predicted MMIs are typically lower by 1–2
units than those estimated from news accounts. This discrepancy is generally consistent with the expected effect of sediment
response, but it could also reflect other factors such as a tendency for media accounts to focus on the most dramatic damage,
rather than the average effects. Our modeling results also suggest, however, that the Bhuj earthquake generated more high-frequency
shaking than is expected for earthquakes of similar magnitude in California, and may therefore have been especially damaging. 相似文献
7.
Russ Evans John Beavan Roger Bilham Geoffrey King 《Geophysical Journal International》1979,57(1):119-135
Summary . We report 35 measurements of Earth strain tides at 16 near-surface sites in Great Britain. This is the first widespread survey undertaken specifically to examine the problem of the inhomogeneity of elastic strain fields near the Earth's surface. Some sites were instrumented intensively in order to examine variations of tidal admittance over distances of several hundred metres, while measurements from single instruments at other sites were compared with theoretically predicted strain tides. After allowing for cavity and topographic effects, our data show variations of up to 50 per cent in tidal admittance. We interpret such large anomalies as being due to variations in the regional elastic parameters of wavelength about a 100 m or less. The data indicate that strain measurements from single instrument sites must be interpreted with caution. 相似文献
8.
An entry in the Tarikh-i-Hassan records that in 883 AD during the reign of King Avantivarman (855–883) an earthquake in Kashmir triggered a landslide that impounded the River Jhelum and flooded the Kashmir Valley. Kalhana’s Rajatarangini provides abundant details about how the ninth century engineer Suyya both cleared the natural dam, drained the valley and instituted numerous irrigation works. We identify the landslide(s) responsible for this Medieval flood and from twentieth century discharge statistics of the Jhelum calculate that it would have taken at least 2 years to flood the Kashmir Valley to near Anantnag. This presents a chronological difficulty, for the causal earthquake could not have occurred in the last 4 months of Avantivarman’s rule, and we conclude that it must have occurred much earlier, perhaps before the start of his reign. The flood occurred during a period of widespread temple building using massive uncemented limestone megablocks, capped by monolithic multi-ton roofs. Many of these magnificent temples, now in ruinous condition, are located close to the shores of the inferred Medieval flood level, suggesting that the transport of construction materials for these temples may have been ferried by barge from distant quarries. Historians and archaeologists have attributed the partial collapse of these temples to malicious damage by subsequent occupants of the valley, but the misalignment of blocks at lower levels within each edifice in recent earthquakes suggests that their lateral offsets are the result of jostling during prolonged shaking in historical earthquakes. From the serendipitous entrapment of datable materials beneath fallen blocks from Kashmir’s ninth century temples we can, in principle, identify the times of historical earthquakes. We chose the ruined Sugandhesa temple near Patan to test this hypothesis. Preliminary results indicate collapse in the tenth or eleventh century, and significant damage in 1885, with at least one intervening earthquake possibly in the seventieth century. 相似文献
9.
Roger Bilham 《Geophysical Journal International》1977,48(3):307-314
Summary. In the past tide gauges have provided valuable information concerning the vertical ground deformation associated with major earthquakes. Although tide-gauge data contains numerous sources of noise; a spacing of less than 40 km between gauges is indicated for a useful study of dilatant behaviour, and a spacing of less than 80 km may be adequate for the study of crustal downwarping in island arcs.
An inexpensive tide gauge is described which is designed to provide a continuous record of sea level with a measurement precision of 1 mm. Hydraulic filtering is incorporated into the instrument in order to attenuate daily tides relative to longer period variations of sea level, The instrument is designed to operate from flashlight batteries for a year unattended and to withstand temporary submersion as might be caused by tsunamis. Several of these sea-level recorders have been installed in seismic gaps in the Aleutians and in the Caribbean. 相似文献
An inexpensive tide gauge is described which is designed to provide a continuous record of sea level with a measurement precision of 1 mm. Hydraulic filtering is incorporated into the instrument in order to attenuate daily tides relative to longer period variations of sea level, The instrument is designed to operate from flashlight batteries for a year unattended and to withstand temporary submersion as might be caused by tsunamis. Several of these sea-level recorders have been installed in seismic gaps in the Aleutians and in the Caribbean. 相似文献
10.
Minutes after the January 12, 2010 Haiti earthquake, most geologists and seismologists assumed that from its shallow teleseismic location and its largely strike-slip mechanism that a significant rupture must have occurred on the transform plate boundary south and west of Port au Prince. Within hours, plans were being made by geologists to map the anticipated rupture and, if possible, to trench it to obtain a record of paleoseismic slip. However, remote sensing images available a few days after the earthquake revealed raised corals and no significant plate boundary slip, and we now know that shallow slip was transpressive and that no surface rupture occurred. A week after the earthquake, it was clear that scientific visits to the region would be much delayed by the continuing needs of emergency response teams and military support who had commandeered access to the airport at Port au Prince. Serendipitously on 20 January, one of the authors accompanied a film crew on a chartered flight from nearby Santo Domingo with the quest to record the tectonic reasons for the disaster and to document the details of structural damage. At the time, there was still no clear idea of whether the transform boundary had a surface rupture, but there was abundant evidence for surface deformation from Google Earth images showing raised corals and collapsed coastlines along the Lêogáne coast. This article briefly describes communications between remote geologists and the ground-based crew who were guided to critical areas in the search for surface deformation using remote sensing data. 相似文献