Amin Esmail Khalil

Regional travel-time residual studies and station correction from 1-D velocity models for some stations around Peninsular Malaysia and Singapore

Abstract We have investigated the average P-wave travel-time residuals for some stations around Southern Thailand, Peninsular Malaysia and Singapore at regional distances. Six years (January, 2010–December, 2015) record of events from central and northern Sumatra was obtained from the digital seismic archives of Integrated Research Institute for Seismology (IRIS). The criteria used for the data selection are designed to be above the magnitude of mb 4.5, depth less than 200 km and an epicentral distance shorter than 1000 km. Within this window a total number of 152 earthquakes were obtained. Furthermore, data were filtered based on the clarity of the seismic phases that are manually picked. A total of 1088 P-wave arrivals and 962 S-wave arrivals were hand-picked from 10 seismic stations around the Peninsula. Three stations IPM, KUM, and KOM from Peninsular Malaysia, four stations BTDF, NTU, BESC and KAPK from Singapore and three stations SURA, SRIT and SKLT located in the southern part of Thailand are used. Station NTU was chosen as the Ref. station because it recorded the large number of events. Travel-times were calculated using three 1-D models (Preliminary Ref. Earth Model PREM (Dziewonski and Anderson, 1981, IASP91, and Lienert et al., 1986) and an adopted two-point ray tracing algorithm. For the three models, we corroborate our calculated travel-times with the results from the use of TAUP travel-time calculation software. Relative to station NTU, our results show that the average P wave travel-time residual for PREM model ranges from −0.16 to 0.45 s for BESC and IPM respectively. For IASP91 model, the average residual ranges from −0.25 to 0.24 s for SRIT and SKLT respectively, and ranges from −0.22 to 0.30 s for KAPK and IPM respectively for Lienert et al. (1986) model. Generally, most stations have slightly positive residuals relative to station NTU. These corrections reflect the difference between actual and estimated model velocities along ray paths to stations and can compensate for heterogeneous velocity structure near individual stations. The computed average travel-time residuals can reduce errors attributable to station correction in the inversion of hypocentral parameters around the Peninsula. Due to the heterogeneity occasioned by the numerous fault systems, a better 1-D velocity model for the Peninsula is desired for more reliable hypocentral inversion and other seismic investigations.

Slope failures evaluation and landslides investigation using 2-D resistivity method

Abstract Slope failure is a complex phenomenon that may caused to landslides. Buildings and infrastructure such as transportation facilities and pipelines located within the boundaries of a landslide can be damaged or destroyed. Slope failure classification and various factors contributing to the instability using 2-D resistivity survey conducted in Selangor, Malaysia are described. Six 2-D resistivity survey lines with 5 m minimum electrode spacing using Pole-dipole array were performed. The data were processed using Res2Dinv and surfer10 software to evaluate the subsurface characteristics. The 2-D resistivity results show that the subsurface consist of two main zones. The first zone was alluvium or highly weathered with resistivity value of 100–1000 Ω m and depth of >30 m. This zone consists of saturated area with resistivity value of 1–100 Ω m and boulders with resistivity value of 1200–7000 Ω m. The second zone with resistivity value of >7000 Ω m was interpreted as granitic bedrock. The study area was characterized by saturated zones, highly weathered zone, highly contain of sand and boulders that will trigger slope failure in the survey area. This will cause to low strength of soil, debris flow and movement of earth. On the basis of the case examples described, 2-D resistivity method is categorized into desirable and useful method in determination of slope failure and future assessments.

Seismic reflection survey at Ayer Hangat site to investigate shallow subsurface structures

Ayer Hangat site is located in the island of Langkawi, northwest Malaysia. The site is characterized by the presence of hot spring. This hot spring is believed to be related to granitic intrusion nearby. Hence the present work is focusing on defining the shallow subsurface structures that control the migration of hot water to the surface. Seismic reflection method is used to achieve the goal of the present study. Forty three shot points were used with an offset of 5m of the nearest geophone. The shot-points interval is set to 1m. Seismograms were recorded on 24 channel TERRALOC instrument. The Geophone interval used was 1m. Conventional seismic data processing scheme was adopted. However, due to the fact that TERRALOC produce SEG2 data files, a script based on Obspy was written and used to convert to SEG-Y format. Afterwards, analyses were carried out using SU Package. The processed data is used to develop a model for the subsurface controlling structures. Such model will help in the understanding of the geothermal hot spring system in the area.