A magnitude (Mw) 7.6 earthquake occurred at 8.55 am (local time) on 8 October 2005 causing extensive damage to buildings, bridges and roads and killing in excess of 87,000 people in the Kashmir region of northern Pakistan. Damage and deaths were also reported from Indian Administered Kashmir and eastern Afghanistan. The most severely affected region was in the epicentral area around Muzaffarabad in Pakistan Administered Kashmir. Reverse or thrust fault rupture on or near the Main Boundary Thrust of the Himalayas has been reported or observed from Chennari in the Jhelum River valley upstream of Muzaffarabad through to Muzaffarabad and over into the Kaghan valley as far north as Balakot, a distance of approximately 60 km. A notable feature of the effects of this earthquake was the asymmetric distribution of landslides across the fault rupture zone. On the downthrown or footwall side (to the southwest) landslide damage was relatively minor – the road from Manshera to Muzaffarabad was open to traffic within 8 hours of the earthquake and required the clearance of only one landslide. On the up-thrown or hanging wall side of the fault rupture zone (to the northeast) the road from Balakot to Kagan required the clearance of 253 landslides and took 24 days. These observations are consistent with the findings of recent strong motion studies.
Ground motion modification (or spectral matching) has been criticized, but has many appealing characteristics and is widely used in practice. Modification of ground motions can be performed in either the time domain or the frequency domain. Depending on the choice of modification technique, modified ground motions can be significantly different from each other as well as from the original ground motion. This paper studies the impact of these differences on seismic geotechnical analyses for two different site profiles using two earthquake scenarios and a total of 20 ground motions. This study shows that the final results are influenced by many factors such as the original (seed) ground motion, the target spectrum, and the local site conditions, in addition to the ground motion modification technique used. The results also show that while both techniques can significantly modify the original ground motion, neither technique is consistently more conservative than the other. Therefore, a general conclusion that a particular technique results in ground motions that yield the largest intensity parameters cannot be made a priori.
The Maleo Producer is located in the Santos' Maleo Field in the Madura Straits, Indonesia. The site is located near the southeastern tip of the Madura Island, north of Java in an area of active tectonics. The driving mechanism for earthquakes in this region is the Sunda Arc subduction zone, a 5,600 km long zone of seismic activity that defines the tectonic boundary between the Indian Ocean part of the Australian tectonic plate and the continental crust of the Eurasian tectonic plate.The Maleo Field is underlain by very soft normally consolidated highly plastic lightweight marine clay requiring a detailed site response analysis that included modeling of soil structure interaction. This paper discusses the development of seismic design criteria for the project and the input parameters for analyses of successively increasing complexity for the evaluation of the platform. The seismic design criteria included development of site-specific seabed response spectra for different return periods for an initial set of response spectrum analysis followed by the development of acceleration time histories for use in the detailed non-linear soil-structure interaction model. The paper also discusses practical considerations in the development of time histories to facilitate reasonable runtime for the global soil-structure interaction analyses.
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