Punya Charusiri

Erosion and Deposition by the 2004 Indian Ocean Tsunami in Phuket and Phang-nga Provinces, Thailand

Abstract The devastating December 26, 2004, tsunami produced abundant geologic effects along the Andaman coast of Thailand. The tsunami inundated the numerous sandy beaches and flowed over the adjacent aeolian dunes. On some of the dunes, the tsunami scoured circular holes 10–30 cm in diameter, and in its waning phases, it coated the holes with mud. The tsunami locally deposited a sand sheet that ranged from 0–30 cm in thickness, with an average thickness of approximately 10 cm. Sedimentary structures within the sand sheet include ripples from inflow and outflow, graded bedding, parallel lamination, and double-layered deposits. Erosion, locally severe, affected sand beaches and tidal inlets. We use these erosional and depositional features to infer the main processes that acted during inundation from the tsunami.

Triassic radiolarian faunas from the Mae Sariang area, northern Thailand and their paleogeographic significane

Abstract Early to Late Triassic (Spathian to Carnian) radiolarians were obtained from the bedded chert sequence of the Mae Sariang Group distributed in northern Thailand. Based on the similarity of radiolarian fauna and petrographical characteristics, it is inferred that the fine-grained siliceous and calcareous sediments of the Mae Sariang Group are equivalent to those belonging to the eastern marginal facies of the Sibumasu Block. Moreover, the occurrence of an early (?) Carnian radiolarian assemblage from bedded chert shows that the closure of the Paleotethys Ocean between the Sibumasu and Indochina Blocks in northern Thailand occurred after the early Carnian.

Deterministic and probabilistic seismic hazard analyses in Thailand and adjacent areas using active fault data

Seismic hazards in Thailand and adjacent areas were analyzed mainly on the basis of geological fault data. We identified 55 active fault zones using remote-sensing data on earthquake source parameters derived from both active fault data and earthquake catalogues. We selected strong ground-motion attenuation models by comparing the application of several candidate models with strong ground-motion data recorded in Thailand. Both deterministic (DSHA) and probabilistic (PSHA) approaches were used—DSHA for the design of critical construction and PSHA for the design of non-critical construction. We also applied two frequency-magnitude models in the PSHA approach: the exponential magnitude distribution model and the characteristic earthquake model. The seismic hazard results obtained using the deterministic and probabilistic approaches are not equivalent. The resulting DSHA map reveals extremely high seismic hazard levels in some areas of Thailand and in surrounding countries, while the PSHA map reveals a seismic hazard distribution similar to that of the DSHA but with lower seismic hazard levels. The areas of high seismic hazard include countries neighboring Thailand, such as Myanmar, Laos, Vietnam, and Indonesia (Sumatra Island), and areas within Thailand itself, primarily those areas in northern, western, and southern Thailand that are dominated by active fault zones.

Enhancement of thematic mapper satellite images for geological mapping of the Cho Dien area, Northern Vietnam

Abstract Information available from the earth science image processing package (ESIPP) software program was applied to enhance the satellite image data of the Cho Dien area, northern Vietnam. The area with dense vegetation covers is dominated by several small Zn–Pb prospects in middle Paleozoic limestone units. Interpretation of satellite image data using the digital enhancement ESIPP program, forms the prime objective of this study, which is to improve the image quality and visual interpretation of regional geology, lineament and structural geology. Thematic mapper of bands 7, 5 and 4 with the false-color composites: blue, green and red, respectively, are considered to be the most appropriate for geologic interpretation. Dark pixel correction is carried out prior to other enhancement analyses which include high-pass filtering, albedo correction, image classification, principle component analysis (PCA) and band ratios. High-pass filtering enhancement is considered to be the most suitable approach for lineament analysis. Albedo is good for differentiating lithology, and image classification is also successfully used for lineament interpretation and discrimination of lithologies but is regarded not better than high-pass filtering and albedo. PCA and ratio of band enhancements are considered not good because there are many disturbed and excavated land areas such as abandoned and current open pits in the concerned area. The result of Landsat interpretation indicate that most lineament structures developed in a roughly N-trending anticlinal structure are in NE-, E- and N-trends. Minor lineaments are in roughly NW-trend, and cross-cutting the NE- and E-trends. Interpretation from enhanced Landsat information also fits very well with field evidences. The interpreted map is slightly different from those of the previous mapping works, particularly with respect to detailed lithological boundaries.

Tectonic significance of detrital chromian spinels in the Permian Nam Duk Formation, central Thailand

Detrital chromian spinels in the Permian Nam Duk Formation, Thailand are examined to determine the petrological characteristics of eroded mafic-ultramafic rocks in the Phetchabun area. Detrital chromian spinels are found as one of accessory heavy minerals from turbiditic sandstones of the Nam Duk Formation. The detrital chromian spinels are generally deep brown to almost opaque in thin section due to their wide compositional variation, and are relatively small, about 20–190 microns across. They sometimes exhibit subhedral to euhedral shapes and rarely have inclusions. Thirty–five grains were chosen for microprobe analysis. They have relatively high Cr contents, the Cr#(=Cr/[Cr+Al] atomic ratio), being mostly higher than 0.50, and up to 0.83. TiO2 contents are generally low but variable from 0.02 to 1.16 wt%, and Fe3+ ratios are consistently low. The relatively high Cr# and low TiO2 contents of the Nam Duk detrital chromian spinels in the Permian sediments indicate their derivation from mafic-ultramafic rocks of are origin. The relatively small and euhedral to subhedral spinels with inclusions especially suggest their provenance from volcanic rocks. It is strongly inferred that igneous rocks, namely volcanics and peridotites, of arc origin were exposed in this region at the Permian at least. The Loei-Phetchabun-Ko Chang volcanic belt, interpreted to have been constructed by several magmatic episodes (Devonian, Permian, Triassic, and Late Tertiary), could be a good candidate for the source of detrital chromian spinels in the Nam Duk Formation.

Paleoearthquake Investigations of the Mae Hong Son Fault, Mae Hong Son Region, Northern Thailand

We applied remote sensing and aerial photographic techniques to a study of the Mae Hong Son Fault (MHSF), located in the Mae Hong Son region, northern Thailand. Several fault lines are recognized in the region, trending mainly NE–SW, NW–SE, and N–S. The main morphotectonic landforms associated with the MHSF are fault scarps, offset streams, linear valleys, triangular facets, offset ridge crests, hot springs, and linear mountain fronts. A trench, a quarry, and a road cut in Caenozoic strata were used to analyze fault geometries in the area. We identified eight paleoearthquake events from trenching, quarry, and road-cut data, and from optically stimulated luminescence (OSL) and thermoluminescence (TL) dating. The OSL and TL ages of the events are: (1) 78,000 yr BP; (2) 68,000 yr BP; (3) 58,000 yr BP; (4) 48,000 yr BP; (5) 38,000 yr BP; (6) 28,000 yr BP; (7) 18,000 yr BP; and (8) 8,000 yr BP. The recurrence interval of seismic events on the MHSF appears to be ca. 10,000 years, and the slip rate was estimated as ca. 0.03–0.13 mm/yr. There is a low possibility of a large earthquake on the MHSF in the near future.

Geochemical characteristics and new eruption ages of ruby-related basalts from southeast Kenya

Two ruby-related basaltic fields were recently discovered in the southeast region of Kenya, exposed in the Nguu and Ngulai Hills vicinities. These fields host abundant deep-seated xenoliths, including corundum-bearing granulites. The basalts are alkaline affinity having compositions from foidrite to basanite. The Ngulai basalts have a wider range of SiO2 (38.2 wt.%–44.8 wt.%) covering those of the Nguu basalts (38.7 wt.%–42.3 wt.%). This overlapping behavior also holds for other major oxides and trace elements, e.g., Al2O3, Na2O, K2O, Cr, Ni, Rb and Ga. The overall OIB-like incompatible patterns with strong K depletion and slight spike of Ti enrichment signatures imply low degrees of partial melting of the upper mantle region source induced under a mantle plume-related process. The K-depletion signature indicates a residual K-bearing phase still retained in the source domain. Chondrite-normalized REE patterns exhibiting strong LREE enrichment without Eu anomalies suggest that plagioclase fractionation is insignificant. New 40Ar/39Ar ages indicate eruption events occurred during the Pleistocene times, which are around 2 Ma for the Ngulai basalts and 0.9 to 1.6 Ma for the Nguu basalts. Clinopyroxene-basalt thermobarometric calculations yield the equilibrium P-T ranges of ∼8-29 kbar and 1 200–1 450 °C.

b-VALUE ANOMALIES ALONG THE NORTHERN SEGMENT OF THE SUMATRA–ANDAMAN SUBDUCTION ZONE: IMPLICATIONS FOR UPCOMING EARTHQUAKES

The potential areas of upcoming earthquakes were investigated along the Northern segment of the Sumatra–Andaman Subduction Zone according to the b-value of the frequency-magnitude distribution. After enhancing the completeness of the earthquake catalogue, two datasets, those recorded during (i) 1980–1994 and (ii) 1980–2003, were tested in order to verify the effective correlation between precursory b-values and the location of subsequent earthquakes. The results confirmed that areas with low b-values agreed well with the locations of the subsequent earthquakes in that region. Accordingly, the present-day dataset from 1980–2010 was carefully evaluated to determine the b-values across the region. Within this spatial investigation, three areas of low b-values and so potential hazards were found. These consisted of the (i) West coast of Myanmar, and (ii) North and (iii) South of the Nicobar Islands. From 2010–2012, a major earthquake with magnitude 7.5 mb was recorded as being generated in the region South of the Nicobar Islands. Thus, attention should be paid to the remaining two until now quiescent areas, and mitigation plans should be raised for both seismic and tsunami hazards.

Geological and engineering analysis of residualsoil for forewarning landslide from highland areain northern Thailand

Abstract One devastating landslide event in northern Thailand occurred in 2006 at Ban Nong Pla village, Chiang Klang highland of Nan province after, a massive amount of residual soil moved from upstream to downstream, via creek tributaries, into a main stream after five days of unusual heavy rainfall. In this paper, the geological and engineering properties of residual soil derived fromsedimentary rocks were analyzed and integrated. Geological mapping, electrical resistivity survey and test pits were carried out along three transect lines together with systematic collection of undisturbed and disturbed residual soil samples. As a result, the average moisture content in soil is 24.83% with average specific gravity of 2.68,whereas the liquid limit is 44.93%, plastic limit is 29.35% and plastic index is 15.58%. The cohesion of soil ranges between 0.096– 1.196 ksc and the angle of internal friction is between 11.51 and 35.78 degrees. This suggests that the toughness properties of soil change when moisture content increases. Results from electrical resistivity survey reveal that soil thicknesses above the bedrock along three transects range from 2 to 9 m. The soil shear strength reach the rate of high decreases in the range of 72 to 95.6% for residual soil from shale, siltstone and sandstone, respectively. Strength of soil decreaseswhen the moisture content in soil increases. Shear strength also decreases when the moisture content changes. Therefore, the natural soil slope in the study area will be stable when the moisture content in soil level is equal to one, but when the moisture content between soil particle increases, strength of soil will decrease resulting in soil strength decreasing.

Probabilistic analysis of the seismic activity and hazard in northern Thailand

The seismic activity and hazard level in northern Thailand, including at the Mae Moh Coal Mine (MMCM), were clarified. For the probability of exceedance (POE), Chiang Mai, Lamphun, and Lampang provinces have a 70–90% and 20–40% POE of a MW-5.0 and MW-6.0 earthquake, respectively, in the next 50 y. In the case of a MW-7.0 earthquake, the POE is less than 10% in the whole study area. Regarding the probabilistic seismic hazard analysis, the ground shaking maps indicated that the southeastern part of the MMCM and northwestern part of Phayao provinces were high hazard areas, with an earthquake ground shaking of around 0.28–0.32g and 0.18–0.24g for a POE of 2% and 10%, respectively, in the next 50 y. In addition, the probability maps revealed that these high hazard areas showed a 60–80% and 30–40% POE of a modified Mercalli intensity (MMI) level III and IV, respectively, in the next 50 y. The low hazard areas of Chiang Mai and Uttaradit provinces had a ground shaking level for a 2% and 10% POE in the next 50 y of around 0.16 and 0.08, respectively, with a POE of a MMI level III or IV of less than 20% each.