Archaeoseismology of the AD 1545 earthquake in Chiang Mai, Northern Thailand

The A.D. 1545 Chiang Mai earthquake in northern Thailand was studied by historical and archaeological sources.The temple Wat Chedi Luang has lost about half of the original 80-metres height due to southward-directed collapse. Twenty-one temple sites – out of 74 visited – has tilted pagodas, up to 5° in various directions, dominated by a SE trend. All damaged temples were built before the 1545 earthquake. We suggest that a city-wide liquefaction event caused tilting. The responsible earthquake possibly occurred along the Doi Suthep Fault within city limits. Possible activity of distant faults is assessed

Recent paleoseismic investigations in Northern and Western Thailand

Recent paleoseismic investigations have identified a number of active faults in Northern and Western Thailand. Northern Thailand is an intraplate basin and range province, comprised of north-south-trending Cenozoic intermontane grabens and half grabens, bounded by north- to northwest-striking normal to normal-oblique faults and northeast-striking left-lateral strike-slip faults. The basin-bounding normal faults are marked by steep, linear range fronts with triangular facets and wineglass canyons and have slip rates of 0.1 to 0.8 mm/yr. Based on limited data, the average vertical displacement-per-event is about 1.0 to 1.5 m. These faults are characterized by recurrence intervals of thousands to tens of thousands of years and are capable of generating earthquakes up to moment magnitude (M) 7, and larger. The northeast-striking strike-slip faults are marked by shutter ridges, and deflected drainages. Slip rates are 3 mm/yr or less. Western Thailand is dissected by a number of northwest- and north-northwest-striking, right-lateral strike-slip faults related to the Sagaing Fault in Myanmar. Although showing much less activity than the faults in neighboring Myanmar, these faults display abundant evidence for late Quaternary movement, including shutter ridges, sag ponds, and laterally offset streams. The slip rate on these faults is estimated to be 0.5 to 2.0 mm/yr. These faults are considered capable of generating maximum earthquakes of up to M 71/2

Cenozoic tectonic evolution of south-eastern Thailand derived from low-temperature thermochronology

Low-temperature thermochronologic techniques, specifically apatite (U-Th)/He and apatite fission track dating were used to reconstruct the thermal history of south-eastern Thailand. This area is intersected by vast and complex fault networks related to the Cenozoic Mae Ping and Three Pagodas Faults. These were identified from satellite imagery and confirmed by field observations. New apatite fission track and apatite (U-Th)/He data were collected from crystalline basement blocks within these fault networks. Ages obtained range from 48 Ma to 24 Ma, with most of the samples clustering between 36 and 24 Ma. Thermal history modelling indicates late Eocene – Oligocene exhumation of the exposed granitic and metamorphic basement rocks in south-eastern Thailand. Exhumation was regional and was contemporaneous with sinistral fault activity during the late Eocene – early Oligocene along the Mae Ping Fault and Three Pagodas Fault. Moreover, this exhumation occurred coevally with a syn-rift phase of intracontinental offshore rift basin and half-graben basin development in the eastern Gulf of Thailand. The phase of exhumation ended in the early Miocene, as a result of the changing plate tectonic forces along the complex plate boundaries of Sundaland

High-resolution mapping using a sub-audio magnetic survey at the Comet Gold Mine,Western Australia

The Comet Gold Mine in the Murchison mineral field lies within the Yilgarn Craton of Western Australia. Gold mineralization in this area is associated with a series of north-northeasterly trending structures, and has a long exploration history with some previous geophysical information. Other exploration information, such as geology and drill hole data, are integrated with the geophysical results to study the geophysical responses and generate a geophysical interpretation map. The response from the sub-audio magnetic (SAM) survey was investigated over an area of 13 sq km. The SAM survey was completed using a transmitter current of 5 - 8 Amp with a 50% duty cycle at 4 Hz frequency, which was considered a good instrumental setting for the Comet area. SAM anomalies were compared to results obtained from other geophysical methods and then integrated with geological data to generate a geophysical interpretation map at a 1 : 5000 scale. The new interpretation of geological units and structures at the Comet area should provide a better understanding of the geological and structural setting for mineralization in the Comet area. Our results show that the Comet Fault represents a faulted limb of the Comet fold structure that has both limbs dipping to the southeast and a plunge to the northeast. Magnetic anomalies associated with sedimentary iron formation (SIF) are considered to be well correlated with some gold bearing horizons and the location of the Comet Fault, which has become more siliceous and has been altered by sulphide minerals and magnetite minerals

Landfill site characterisation at Kham Bon village, Muang district, Khon Kaen province, NE Thailand

The aim of the study is to characterise the Kham Bon landfill site. Hydrogeological and geochemical surveys were conducted and four boreholes were drilled. The hydraulic properties of the aquifer were tested, and soil, surface water and groundwater samples were collected at various times in the year. The physical and chemical properties of the samples, especially heavy metals, were analysed. The results indicated that Cd, Cr, Pb, Cu and Zn occurred in significant concentrations in the soil. The concentrations of Pb, Fe and Mn are high in surface water and groundwater. Moreover, the groundwater chemistry of the shallow aquifer was characterised by high concentrations of some ions. The major factors controlling leachate production and migration in this area are the seasonal variations in precipitation, the site topography, which controls the runoff patterns, and the soil type, which affects infiltration and solute transport to the water table. Copyright © 2009, Inderscience Publishers

Timing of metamorphism of the Lansang gneiss and implications for left-lateral motion along the Mae Ping (Wang Chao) strike-slip fault, Thailand

The Mae Ping fault (MPF), western Thailand, exhibits dominantly left-lateral strike-slip motion and stretches for >600. km, reportedly branching off the right-lateral Sagaing fault in Myanmar and extending southeast towards Cambodia. Previous studies have suggested that the fault assisted the large-scale extrusion of Sundaland that occurred during the Late Eocene-Early Oligocene, with a geological offset of ~120-150. km estimated from displaced high-grade gneisses and granites of the Chiang Mai-Lincang belt. Exposures of high-grade orthogneiss in the Lansang National Park, part of this belt, locally contain strong mylonitic textures and are bounded by strike-slip ductile shear zones and brittle faults. Geochronological analysis of monazite from a sample of sheared biotite-K-feldspar orthogneiss suggests two episodes of crystallization, with core regions documenting Th-Pb ages between c. 123 and c. 114. Ma and rim regions documenting a significantly younger age range between c. 45-37. Ma. These data are interpreted to represent possible magmatic protolith emplacement for the Lansang orthogneiss during the Early Cretaceous, with a later episode of metamorphism occurring during the Eocene. Textural relationships provided by in situ analysis suggest that ductile shearing along the MPF occurred during the latter stages of, or after, this metamorphic event. In addition, monazite analyzed from an undeformed garnet-two-mica granite dyke intruding metamorphic units at Bhumipol Lake outside of the Mae Ping shear zone produced a Th-Pb age of 66.2. ±. 1.6. Ma. This age is interpreted to date the timing of dyke emplacement, implying that the MPF cuts through earlier formed magmatic and high-grade metamorphic rocks. These new data, when combined with regional mapping and earlier geochronological work, show that neither metamorphism, nor regional cooling, was directly related to strike-slip motion. © 2013 Elsevier Ltd

Timing of metamorphism of the Lansang gneiss and implications for left-lateral motion along the Mae Ping (Wang Chao) strike-slip fault, Thailand

The Mae Ping fault (MPF), western Thailand, exhibits dominantly left-lateral strike-slip motion and stretches for >600 km, reportedly branching off the right-lateral Sagaing fault in Myanmar and extending southeast towards Cambodia. Previous studies have suggested that the fault assisted the large-scale extrusion of Sundaland that occurred during the Late Eocene–Early Oligocene, with a geological offset of ∼120–150 km estimated from displaced high-grade gneisses and granites of the Chiang Mai–Lincang belt. Exposures of high-grade orthogneiss in the Lansang National Park, part of this belt, locally contain strong mylonitic textures and are bounded by strike-slip ductile shear zones and brittle faults. Geochronological analysis of monazite from a sample of sheared biotite-K-feldspar orthogneiss suggests two episodes of crystallization, with core regions documenting Th–Pb ages between c. 123 and c. 114 Ma and rim regions documenting a significantly younger age range between c. 45–37 Ma. These data are interpreted to represent possible magmatic protolith emplacement for the Lansang orthogneiss during the Early Cretaceous, with a later episode of metamorphism occurring during the Eocene. Textural relationships provided by in situ analysis suggest that ductile shearing along the MPF occurred during the latter stages of, or after, this metamorphic event. In addition, monazite analyzed from an undeformed garnet-two-mica granite dyke intruding metamorphic units at Bhumipol Lake outside of the Mae Ping shear zone produced a Th–Pb age of 66.2 ± 1.6 Ma. This age is interpreted to date the timing of dyke emplacement, implying that the MPF cuts through earlier formed magmatic and high-grade metamorphic rocks. These new data, when combined with regional mapping and earlier geochronological work, show that neither metamorphism, nor regional cooling, was directly related to strike-slip motion

Drastic shrinking of the Hadley circulation during the mid-Cretaceous Supergreenhouse

Understanding the behavior of the global climate system during extremely warm periods is one of the major themes of paleoclimatology. Proxy data demonstrate that the equator-to-pole temperature gradient was much lower during the mid-Cretaceous "supergreenhouse" period than at present, implying larger meridional heat transport by atmospheric and/or oceanic circulation. However, reconstructions of atmospheric circulation during the Cretaceous have been hampered by a lack of appropriate datasets based on reliable proxies. Desert distribution directly reflects the position of the subtropical high-pressure belt, and the prevailing surface-wind pattern preserved in desert deposits reveals the exact position of its divergence axis, which marks the poleward margin of the Hadley circulation. We reconstructed temporal changes in the latitude of the subtropical high-pressure belt and its divergence axis during the Cretaceous based on spatio-temporal changes in the latitudinal distribution of deserts and prevailing surface-wind patterns in the Asian interior. We found a poleward shift in the subtropical high-pressure belt during the early and late Cretaceous, suggesting a poleward expansion of the Hadley circulation. In contrast, an equatorward shift of the belt was found during the mid-Cretaceous "supergreenhouse" period, suggesting drastic shrinking of the Hadley circulation. These results, in conjunction with recent observations, suggest the existence of a threshold in atmospheric CO<sub>2</sub> level and/or global temperature, beyond which the Hadley circulation shrinks drastically