Geology topics

K. Sieh

Publications and source records attributed to K. Sieh.

5 recordsLinked to original sources

USGS2006

Uplift and subsidence associated with the great Aceh-Andaman earthquake of 2004

Rupture of the Sunda megathrust on 26 December 2004 produced broad regions of uplift and subsidence. We define the pivot line separating these regions as a first step in defining the lateral extent and the downdip limit of rupture during that great Mw ??? 9.2 earthquake. In the region of the Andaman and Nicobar islands we rely exclusively on the interpretation of satellite imagery and a tidal model. At the southern limit of the great rupture we rely principally on field measurements of emerged coral microatolls. Uplift extends from the middle of Simeulue Island, Sumatra, at ??? 2.5??N, to Preparis Island, Myanmar (Burma), at ??? 14.9??N. Thus the rupture is ??? 1600 km long. The distance from the pivot line to the trench varies appreciably. The northern and western Andaman Islands rose, whereas the southern and eastern portion of the islands subsided. The Nicobar Islands and the west coast of Aceh province, Sumatra, subsided. Tilt at the southern end of the rupture is steep; the distance from 1.5 m of uplift to the pivot line is just 60 km. Our method of using satellite imagery to recognize changes in elevation relative to sea surface height and of using a tidal model to place quantitative bounds on coseismic uplift or subsidence is a novel approach that can be adapted to other forms of remote sensing and can be applied to other subduction zones in tropical regions. Copyright 2006 by the American Geophysical Union.

Journal of Geophysical Research B: Solid Earth↗

USGS2004

Paleogeodetic records of seismic and aseismic subduction from central Sumatran microatolls, Indonesia

We utilize coral microatolls in western Sumatra to document vertical deformation associated with subduction. Microatolls are very sensitive to fluctuations in sea level and thus act as natural tide gauges. They record not only the magnitude of vertical deformation associated with earthquakes (paleoseismic data), but also continuously track the long-term aseismic deformation that occurs during the intervals between earthquakes (paleogeodetic data). This paper focuses on the twentieth century paleogeodetic history of the equatorial region. Our coral paleogeodetic record of the 1935 event reveals a classical example of deformations produced by seismic rupture of a shallow subduction interface. The site closest to the trench rose 90 cm, whereas sites further east sank by as much as 35 cm. Our model reproduces these paleogeodetic data with a 2.3 m slip event on the interface 88 to 125 km from the trench axis. Our coral paleogeodetic data reveal slow submergence during the decades before and after the event in the areas of coseismic emergence. Likewise, interseismic emergence occurred before and after the 1935 event in areas of coseismic submergence. Among the interesting phenomenon we have discovered in the coral record is evidence of a large aseismic slip or "silent even" in 1962, 27 years after the 1935 event. Paleogeodetic deformation rates in the decades before, after, and between the 1935 and 1962 events have varied both temporally and spatially. During the 25 years following the 1935 event, submergence rates were dramatically greater than in prior decades. During the past four decades, however, rates have been lower than in the preceding decades, but are still higher than they were prior to 1935. These paleogeodetic records enable us to model the kinematics of the subduction interface throughout the twentieth century. Copyright 2004 by the American Geophysical Union.

Journal of Geophysical Research B: Solid Earth↗

USGS2003

The 2002 Denali fault earthquake, Alaska: A large magnitude, slip-partitioned event

The MW (moment magnitude) 7.9 Denali fault earthquake on 3 November 2002 was associated with 340 kilometers of surface rupture and was the largest strike-slip earthquake in North America in almost 150 years. It illuminates earthquake mechanics and hazards of large strike-slip faults. It began with thrusting on the previously unrecognized Susitna Glacier fault, continued with right-slip on the Denali fault, then took a right step and continued with right-slip on the Totschunda fault. There is good correlation between geologically observed and geophysically inferred moment release. The earthquake produced unusually strong distal effects in the rupture propagation direction, including triggered seismicity.

Science↗

USGS2003

Paleoseismic evidence of characteristic slip on the Western segment of the North Anatolian fault, Turkey

We have conducted a paleoseismic investigation of serial fault rupture at one site along the 110-km rupture of the North Anatolian fault that produced the M w 7.4 earthquake of 17 August 1999. The benefit of using a recent rupture to compare serial ruptures lies in the fact that the location, magnitude, and slip vector of the most recent event are all very well documented. We wished to determine whether or not the previous few ruptures of the fault were similar to the recent one. We chose a site at a step-over between two major strike-slip traces, where the principal fault is a normal fault. Our two excavations across the 1999 rupture reveal fluvial sands and gravels with two colluvial wedges related to previous earthquakes. Each wedge is about 0.8 m thick. Considering the processes of collapse and subsequent diffusion that are responsible for the formation of a colluvial wedge, we suggest that the two paleoscarps were similar in height to the 1999 scarp. This similarity supports the concept of characteristic slip, at least for this location along the fault. Accelerator mass spectrometry (AMS) radiocarbon dates of 16 charcoal samples are consistent with the interpretation that these two paleoscarps formed during large historical events in 1509 and 1719. If this is correct, the most recent three ruptures at the site have occurred at 210- and 280-year intervals.

North Anatolian fault↗

USGS1993

Near-field investigations of the Landers earthquake sequence, April to July 1992

The Landers earthquake, which had a moment magnitude ( M w ) of 7.3, was the largest earthquake to strike the contiguous United States in 40 years. This earthquake resulted from the rupture of five major and many minor right-lateral faults near the southern end of the eastern California shear zone, just north of the San Andreas fault. Its M w 6.1 preshock and M w 6.2 aftershock had their own aftershocks and foreshocks. Surficial geological observations are consistent with local and far-field seismologic observations of the earthquake. Large surficial offsets (as great as 6 meters) and a relatively short rupture length (85 kilometers) are consistent with seismological calculations of a high stress drop (200 bars), which is in turn consistent with an apparently long recurrence interval for these faults.

California↗