This paper studied the effects of Coulomb stress in understanding the proximity to failure on the Palu-Koro fault system. An earthquake occurred on a large strike-slip fault in the northern part of Sulawesi Island, Indonesia, on September 28, 2018. Coulomb stress increased by approximately 1 bar, corresponding closely to the locations of aftershocks and areas where stress dropped by more than 10 bars. Based on the focal mechanisms of the aftershocks and source models of the main shock, the Coulomb failure stress changes on both of the focal mechanism nodal planes are calculated. Additionally, we calculated the changes in Coulomb stress on the focal sources of each aftershock. Our stress model indicates a positive correlation within the areas of the extended Coulomb stress caused by the combination of seismic activities. We investigated the Coulomb stress as a possible origin for the aftershocks, which are most likely to slip optimally oriented for failure due to the local stress field generated by the mainshock. The Palu 7.5 earthquake led to the distribution of surface displacements. Moreover, calculated horizontal displacement increased in the NW-SW direction, ranging from 1 to 1.3 meters. The stress maps included in this paper are crucial in predicting the expected locations of future aftershocks and mitigating the potential for earthquakes.

Keywords: Coulomb stress, stress inversion, deformation, earthquake, Palu, Indonesia

REFERENCES

Ahadov B., Jin S. Effects of Coulomb stress change on Mw> 6 earthquakes in the Caucasus region. Physics of the Earth and Planetary Interiors, Vol. 297, 106326, 2019, https//doi.org/ 10.1016/ j.pepi.2019.106326.  

Bellier O., Sébrier M., Beaudouin T., Villeneuve M., Braucher R., Bourles D., Siame L., Putranto E., Pratomo I. High slip rate for a low seismicity along the Palu‐Koro active fault in central Sulawesi (Indonesia). Terra Nova, Vol. 13, No. 4, 2001, pp. 463-470, DOI:10.1046/j.1365-3121.2001.00382.

Ekström G., Nettles M., Dziewoński A. The global CMT project 2004-2010: Centroid-moment tensors for 13,017 earthquakes. Physics of the Earth and Planetary Interiors, Vol. 200-201, 2012, pp. 1-9, DOI: 10.1016/J.pepi.2012.04.002.

Gephart J.W., Forsyth D.W. An improved method for determining the regional stress tensor using earthquake focal mechanism data: application to the San Fernando earthquake sequence. Journal of Geophysical Research: Solid Earth, Vol. 89, 1984, pp. 9305-9320, https://doi.org/10.1029/JB089iB11p09305.

Hardebeck J.L., Nazareth J.J., Hauksson E. The static stress change triggering model: Constraints from two southern California aftershock sequences. Journal of Geophysical Research: Solid Earth, Vol. 103, No. B10, 1998, pp. 24427-24437.

Hardebeck J.L., Okada T. Temporal stress changes caused by earthquakes: A review. Journal of Geophysical Research: Solid Earth, Vol. 123, No. 3-4, 2018, pp. 1350-1365, DOI:10.1002/2017jBO 14617.

Harris R.A. Introduction to special section: Stress triggers, stress shadows, and implications for seismic hazard. J. Geophys. Research., Vol. 103, No. B10, 1998, pp. 24347-24358.

King G.C., Stein R.S., Lin J. Static stress changes and the triggering of earthquakes. Bulletin of the Seismological Society of America, Vol. 84, No. 3, 1994, pp. 935-953.

King G.C.P. Fault interaction, earthquake stress changes, and the evolution of seismicity.  Treatise on Geophysics, Vol. 4, 2007, pp. 225-255, DOI:10.1016/B978-044452748-6.00069-9.

Kreemer C., Holt W.E, Goes S., Govers R. Active deformation in eastern Indonesia and the Philippines from GPS and seismicity data. Journal of Geophysical Research: Solid Earth, Vol. 105, No. B1, 2000, pp. 663-680.

Lin J., Stein R.S. Stress triggering in thrust and subduction earthquakes and stress interaction between the southern San Andreas and nearby thrust and strike‐slip faults. Journal of Geophysical Research: Solid Earth, Vol. 109, No. B2, 2004, 19 p., DOI:org/10.1029/2003JB002607

Michael A.J. Determination of stress from slip data: faults and folds. Journal of Geophysical Research: Solid Earth, Vol. 89, No. B13, 1984, pp. 11517-11526, DOI:10.1029/JBO89i13p11517.

Reasenberg P.A., Simpson R.W. Response of regional seismicity to the static stress change produced by the Loma Prieta earthquake. Science, Vol. 255, No. 5052, 1992, pp. 1687-1690, DOI:10.1126/science 255.5052.1687.

Roeloffs E.A. Hydrologic precursors to earthquakes: A review. Pure and applied geophysics, Vol. 126, 1988, pp. 177-209.

Silver E.A., Moore J.C. The Molucca sea collision zone, Indonesia. Journal of Geophysical Research: Solid Earth, Vol. 83, 1978, pp. 1681-1691.

Simons W., van Loon D., Waspersdorf A., Ambrosius B., Kahar J., Abidin H., Sarsito D., Vigny C., Abu S.H., Morgan P. Geodynamics of SE Asia: First results of the Sulawesi 1998 GPS campaign. In: Geodesy Beyond 2000, Springer. 2000, pp. 271-277.

Socquet A., Simons W., Vigny C., McCaffrey R., Subarya C., Sarsito D., Ambrosius B., Spakman W. Microblock rotations and fault coupling in SE Asia triple junction (Sulawesi, Indonesia) from GPS and earthquake slip vector data. Journal of Geophysical Research: Solid Earth,Vol. 111, No. B8,  2006, DOI: org/10.1029JBOO3963.

Stevens C., McCaffrey R., Bock Y., Genrich J., Subarya C., Puntodewo S. and Vigny C. Rapid rotations about a vertical axis in a collisional setting revealed by the Palu fault, Sulawesi, Indonesia. Geophysical Research Letters, Vol. 26, No. 17, 1999, pp. 2677-2680, DOI:org/10.1029/1999GE008344.

Strader A.E. The effects of Coulomb stress change on Southern California earthquake forecasting. UCLA. ProQuest ID: Strader_ucla_0031D_12803. Merritt ID: ark:/13030/ m58d22pj,  2014,166 , DOI:10.13140/RG.22.36576.48647.

Steacy S., Nalbant S.S., McCloskey J., Nostro C., Scotti O., Baumont D. Onto what planes should Coulomb stress perturbations be resolved?  J. Geophys. Res., Vol. 110, No. B5, 2005, B05S15, DOI: 10.1029/2004JBOO3356.

Stein R.S., King G.C.P., Lin J. Change in failure stress on the southern San Andreas fault system caused by the 1992 Magnitude = 7.4 Landers earthquake. Science, Vol. 258, 1992, pp. 1328-1332, DOI:10/1126science.258.5086.1328.

Toda S., Stein R.S., Reasenberg P.A., Dieterich J.H., Yoshida A. Stress transferred by the 1995 Mw= 6.9 Kobe, Japan, shock: Effect on aftershocks and future earthquake probabilities. Journal of Geophysical Research: Solid Earth, Vol. 103, No. 10, 1998, pp. 24543-24565, DOI:org/10.1029/98J600765.

Toda S., Stein R.S., Richards‐Dinger K., Bozkurt S.B. Forecasting the evolution of seismicity in southern California: Animations built on earthquake stress transfer. Journal of Geophysical Research: Solid Earth, Vol. 110, No. 5, 2005, 17 p., DOI: 10.1029/2004JBOO3415.

Tregoning P., McQueen H., Lambeck K., Jackson R., Little R., Saunders S., Rosa R., Present-day crustal motion in Papua New Guinea. Earth, planets and space, Vol. 52, No. 10, 2000, pp. 727-730.

Vavryčuk V. Iterative joint inversion for stress and fault orientations from focal mechanisms. Geophysical Journal International, Vol. 199, No. 1, 2014, pp. 69-77, DOI: org/1093/gji/ggu224.

Wallace L.M., Stevens C., Silver E., McCaffrey R., Loratung W., Hasiata S., Stanaway R., Curley R., Rosa R., Taugaloidi J. GPS and seismological constraints on active tectonics and arc‐continent collision in Papua New Guinea: Implications for mechanics of microplate rotations in a plate boundary zone. Journal of Geophysical Research: Solid Earth, Vol. 109, No. 5,  2004, DOI: 10.1029/2003JBOO2481

Wells D.L., Coppersmith K.J. New empirical relationships among magnitude, rupture length, rupture width, rupture area, and surface displacement. Bulletin of the seismological Society of America, Vol. 84, 1994, pp. 974-1002, DOI:org/10.1785/ BSSA0840040974.

Wessel P., Smith W.H., Scharroo R., Luis J., Wobbe F. The generic mapping tools: improved version released. EOS, Transactions American Geophysical Union, Vol. 94, No. 45, 2013, pp. 409-410, DOI: 10.1002/2013EO450001.

Walpersdorf A., Rangin C., Vigny C. GPS compared to long-term geologic motion of the north arm of Sulawesi. Earth and Planetary Science Letters, Vol. 159, 1998, pp. 47-55.