Could you please rephrase your question? I can't understand what you mean.

Dear Dr. Gianvito Scaringi

Going through a paper/article, an earthquake event in Sichuan province, China triggered landslides in such a way that their distribution has been documented as the number of landslides along road triggered by this particular event were much higher than the landslides triggered along river or stream. When I totally read this paper, an idea of "instan effect" came in my mind so put it on RG as question for landslide experts to think about it further.

Following

I do not think the term "instant effect" is appropriate to describe this particular pattern. If you want, coseismic landslides in general could be regarded as the (quasi)instantaneous response of the slopes to the seismic shaking.

With specific regard to the pattern observed in the Jiuzhaigou earthquake (I think you are referring to that, aren't you?) the concentration of landslides along roadways might suggest that earthworks were done without properly accounting for the seismicity in the area. However, roads usually run nearby the river network in this region, thus the two controls appear closely correlated. Your observation that "the number of landslides along road triggered by this particular event were much higher than the landslides triggered along river or stream" does not seem correct for the Jiuzhaigou area, having seen the data.

Dear Dr. Gianvito Scaingi

The statement "Number of co-seismic landslides are much higher than the co-seismic landslides along a river or a stream" is picked from the paper.

Next time I will refer that paper.