3-D magnetotelluric imaging of the Phayao Fault Zone, Northern Thailand: Evidence for saline fluid in the source region of the 2014 Chiang Rai earthquake
“…Fig. 15Illustrating the fault F3 interpretation from gravity data corresponds well with previous studies of Magnetotellurics (MT) map from Boonchaisuk et al. (2017) that interpreted the faults on the eastern and northern parts of the Mae Suai Basin.…”
Section: Discussionsupporting
confidence: 86%
“…(2017) (Fig. 2b) and the larger scale high conductive fault zone of the Magnetotellurics inversion solution by Boonchaisuk et al. (2017) are also compatible with the ENE-WSE orientation of Fault F3 (Figs.…”
The Mae Suai Basin, an intermountain basin in northern Thailand, became an area of interest in 2014 following the M6.1 earthquake that reactivated the ENE-WSW trending Mae Loa Fault. This fault is associated with the Cenozoic rifting. Terrestrial gravity modelling is a suitable method to visualize subsurface geometry and understand its structural control related to the recent earthquakes. Six hundred twenty-seven terrestrial gravity stations with a spacing of ∼500 m were collected; standard gravity correction methods were applied with a density reduction of 2.67 g/cm
3
to produce the residual Complete Bouguer anomaly (CBA). The residual CBA map reveals a NNE-SSW striking basin, showing gravity lows are located within the basin. The gravity highs cover regions of Triassic granite intrusions to the west and Silurian-Devonian metasedimentary and Carboniferous sedimentary basements to the east. Structural edge detections and basin depth estimates indicate the main fault lineaments lie ENE-SWS and NNE-SSW striking along the eastern and northern margins respectively. These faults may act as splay faults of the active sinistral Mae Loa fault. The gravity models suggest that the Mae Suai Basin is an asymmetrical half-graben with a maximum depth of ∼770 m and a range of basin sediments from 1.9 to 2.3 g/cm
3
. The depocentre is located near the eastern boundary faults. The structural patterns present the rifting has formed within an extensional transfer zone that relates to a releasing bend fault in NNE-SSW trend, linked by the sinistral Mae Loa Fault in NE-SW trend. The E-W maximum of extension in the transfer zone is formed under the activation of the major Cenozoic strike-slip faults in Northern Thailand.
“…Fig. 15Illustrating the fault F3 interpretation from gravity data corresponds well with previous studies of Magnetotellurics (MT) map from Boonchaisuk et al. (2017) that interpreted the faults on the eastern and northern parts of the Mae Suai Basin.…”
Section: Discussionsupporting
confidence: 86%
“…(2017) (Fig. 2b) and the larger scale high conductive fault zone of the Magnetotellurics inversion solution by Boonchaisuk et al. (2017) are also compatible with the ENE-WSE orientation of Fault F3 (Figs.…”
The Mae Suai Basin, an intermountain basin in northern Thailand, became an area of interest in 2014 following the M6.1 earthquake that reactivated the ENE-WSW trending Mae Loa Fault. This fault is associated with the Cenozoic rifting. Terrestrial gravity modelling is a suitable method to visualize subsurface geometry and understand its structural control related to the recent earthquakes. Six hundred twenty-seven terrestrial gravity stations with a spacing of ∼500 m were collected; standard gravity correction methods were applied with a density reduction of 2.67 g/cm
3
to produce the residual Complete Bouguer anomaly (CBA). The residual CBA map reveals a NNE-SSW striking basin, showing gravity lows are located within the basin. The gravity highs cover regions of Triassic granite intrusions to the west and Silurian-Devonian metasedimentary and Carboniferous sedimentary basements to the east. Structural edge detections and basin depth estimates indicate the main fault lineaments lie ENE-SWS and NNE-SSW striking along the eastern and northern margins respectively. These faults may act as splay faults of the active sinistral Mae Loa fault. The gravity models suggest that the Mae Suai Basin is an asymmetrical half-graben with a maximum depth of ∼770 m and a range of basin sediments from 1.9 to 2.3 g/cm
3
. The depocentre is located near the eastern boundary faults. The structural patterns present the rifting has formed within an extensional transfer zone that relates to a releasing bend fault in NNE-SSW trend, linked by the sinistral Mae Loa Fault in NE-SW trend. The E-W maximum of extension in the transfer zone is formed under the activation of the major Cenozoic strike-slip faults in Northern Thailand.
“…On 5 May 2014, the Mw 6.2 Mae Lao earthquake occurred in this region of mapped faults, within an area inferred to have high fluid content (Boonchaisuk et al, 2017). The event produced a maximum PGA of 0.30 g measured on top of a dam 15 km from the epicenter and 0.13 g at a ground-based station 27 km from the epicenter (Ornthammarath and Warnitchai, 2015), consistent with the previously estimated hazard probabilities.…”
“…The Magnetotelluric (MT) method was chosen in this case, considering that this method is capable of reaching depths of tens of kilometers [5] and still displays the boundaries between different resistivity features clearly. This method can also detect various underground features that appear as resistivity anomalies, including faults [6], alteration zones [7], karst channels [8], and saline fluids [9]. The MT method has been used in various studies of detailed underground structures, especially in cases reaching depths of thousands of meters or more, such as basin investigations [10][11][12], aquifers [13], geothermal systems [14], volcanic systems [15], even cratons [5] [16].…”
Previous studies in Gondang Subdistricthave identified underground mud reservoirnear a rock intrusion, while another study near Gondang Subdistrict has identified deep fault structures. This study will identify the distribution and characteristics of possible geological features in the area using magnetotelluric (MT) method to further describe the relationship between the geological features related to local geology. MT data measurements were conducted on 7 stations alonga north-south line, then modelled in 2D using nonlinear conjugate gradient algorithm. The model was used to describe the subsurface resistivity distribution and to identify the geological features. The results show 5 resistive zones (20–1250 Ω⋅m) and 4 conductive zones (≤10 Ω⋅m). The former consist of 4 vertical zones, 1 vertical zone deeper than 5 km, and 1 horizontal zone near the surface. 2 conductive zones surround a resistive zone, while 2 others stretch below the horizontal resistive zone. The vertical resistive zones are interpreted as andesite intrusions, and the horizontal one as volcanic breccia. The conductive zones are interpreted consisting of tuff and marl with possible saline water content. 3 vertical intrusions are thought to have the same source, and all vertical intrusions are suspected to co-occurr with the Pandan Volcano intrusion.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
