## 3 Coulomb Stress Changes Computed on Nodal Planes  
We present here the high-quality focal mechanism solutions of six \(M\geq 6\) aftershocks from USGS (Table 1). All of the aftershocks are within the depth range of 0-50 km, bounded by 0.3\({}^{\circ}\)-0.9\({}^{\circ}\) N latitude and 79\({}^{\circ}\)-81\({}^{\circ}\) W longitude. Based on the finite fault model of the \(M\) 7.8 mainshock inverted by [PERSON] [35], we compute the coulomb stress changes on both nodal planes of each subsequent aftershock in their rake directions (Figure 3). We simulate the \(M\) 7.8 mainshock as dislocations in an elastic half-space and compute the resulting static stress changes. Our computational results are precise in the near field where the details of the slip distribution are critical. Correspondingly, the details of the slip distribution in the far field become less important than the total moment of the earthquake and the average orientation of the rupture plane [39]. Coulomb stress changes exhibit a lobed pattern of alternating positive and negative stress changes on the receiver fault planes or nodal planes. The computation of coulomb stress changes on both of the nodal planes are a direct test of the coulomb hypothesis. Figure 2: The finite fault model of the \(M\) 7.8 coastal Ecuador earthquake (unit: m). It is subdivided in 15 patches along the strike and 16 patches along the slip. Each patch is 13 \(\times\) 9 km\({}^{2}\). The blue line within each patch represents the slip direction. The bar on the right indicates the slip amount of each patch. Figure 3: \(Cont.\)  
Figure 3 illustrates the coulomb stress changes triggered by the \(M\) 7.8 mainshock on both nodal planes of the six \(M\geq 6\) aftershocks. As illustrated in Figure 3, the stress field figures for each aftershock are completely different because two different nodal planes are represented. Each figure shows the characteristic areas of coulomb stress increases and areas of coulomb stress decreases caused by the \(M\) 7.8 mainshock. The distributions of the six \(M\geq 6\) aftershocks are consistent with these stress change patterns. Rises in coulomb stress appear to be sufficient to trigger aftershock events, while coulomb stress reductions effectively inhibit them. Among the six \(M\geq 6\) aftershocks, five of the hypocenters plotted fall in regions of positive stress changes. Conversely, only one hypocenter falls within the stress shadow of the mainshock, as shown in Figure 3i. Overall, we observe that the vast majority of the aftershocks undergo positive coulomb stress change, which would promote or trigger rupture. These findings suggest that the \(M\) 7.8 mainshock may have triggered the six \(M\geq 6\) aftershocks. It should be noted that the focal mechanism solutions display geometry similar to the six \(M\geq 6\) aftershocks. Small uncertainties could remarkably affect the computation results. Therefore, we explore the coulomb stress change on the focal mechanism solutions given by USGS. We assume that each \(M\geq 6\) aftershock has a focal mechanism solution consistent with the regional tectonic stress field. Figure 3: Illustration of coulomb stress changes on both nodal planes of six \(M\geq 6\) aftershocks triggered by the 2016 Ecuador \(M\) 7.8 earthquake based on [PERSON]’s finite fault model (unit: bar).