Seismic Tomographic Imaging: Algorithm and Files

Published: 6 March 2020| Version 3 | DOI: 10.17632/j2c8nmmnzt.3
Abel Osagie, Ismail Abir


List of input and output files 1. PICKS-BISC-1964-2017: Arrival time data the bulletin of International Seismological Center (ISC) for earthquakes that have occurred around the Sumatran Fault System spanning latitudes 10º N - 10º S and longitudes 93º E-114º E. 2. SFILE-06-18: Hand-picked data using SEISAN software. Waveform is obtained from Incorporated Research Institutions for Seismology (IRIS) 3. Global list of seismic stations and their locations (courtesy ISC) 4. A_VMD2: The algorithm used to generated the final model 5. A11-MODEL-DEP-SLICE: Output file for representative depths 6. A11-MODEL-LAT-SLICE: Output file for North-South vertical cross-sections 7. A11-MODEL-LON-SLICE: Output file for East-West vertical cross-sections 8. A11_MODEL-3D: Output file for 3-D model of the study region 9. A_VMD.INC: A common file required by many subroutines in the main algorithm 10. EVENTS: All earthquakes used in the study 11. A13-RESIDUALS: Computed traveltime residuals for all stations and for all events. 12. List of 1-D velocity models. (the iasp91 model is used) Tomographic results show low-velocity (low-V) anomalies that reflect both accretion and possibly, asthenospheric upwelling associated with subduction of the Australian plate beneath the Eurasian plate around the Sumatra subduction zone (SSZ). The prominent low-V anomaly is thickest around the Conrad, extending beneath Malacca Strait and parts of Peninsular Malaysia, but disappears around the Moho (which appears to be less than 35 km) in the region. Below the Moho, the subducting Australian slab, represented by a high-velocity (high-V) anomaly, trends in the orientation of Sumatra. At these depths, the eastern shorelines of Sumatra, most parts of Malacca Strait and the west coast of Peninsular Malaysia show varying degrees of positive velocity anomalies. We consider that asthenospheric upwelling around the SSZ provide heat source for the 40 or more hot springs distributed North-South in Peninsular Malaysia. Different East-West and North-South cross-sections reveal the subsurface anomalies at various parts of the region. The predominant low-V anomaly is less than 35 km in depth but other low-V anomalies are deeper.


Steps to reproduce

Data used in this work is obtained from the Incorporated Research Institutions for Seismology (IRIS) and the bulletin of International Seismological Center (BISC). The earthquakes (magnitude ≥ 3.0 mb) are confined to the top 100 km in focal depths, latitude ranges from 10º N - 10º S and longitude spans 93º E - 115º E. A software (JWEED) developed by seismology department at the University of South Carolina (USC, 2012) is used to retrieve waveforms from the IRIS free online data archive for the period between 2006 and 2018. This was the period of good waveform data during the time of data collection. In 2018, this study also obtained all available arrival time data from BISC between 1964 and 2016. The BISC data ended in 2016 as at the time of data collection for this study. Review of the BISC data is usually about 24 months behind time because arrival times are manually checked by BISC analysts. Later in 2019, the revised BISC dataset until mid-2017 was added to the dataset. Hand-picked phases from the IRIS waveforms between 2017 and 2018 are combined with the dataset from the BISC to obtain a total of 16,196 events with 109,260 first arrivals p-waves


University of Abuja