Answer:
Dried-up creek beds across the area have (has) started flowing again thanks to the earthquake that shook our community last month The quake displaced groundwater which has worked its way to the surface.
Step-by-step explanation:
Subject-verb agreement refers to the relationship between the subject and the verb of the sentence. And according to this agreement, they must agree with each other with regards to the number, i.e, if the subject is singular, so will the verb be and accordingly.
In the given passage, the subject-verb agreement is wrong in the line "Dried-up creek beds across the area has started...". Here, the verb "has" will be changed to "have", with regards to the subject "dried-up creek beds" which is plural, and thus the use of the singular "has" is wrong.
Thus, the incorrect verb is "has" and should be replaced by "have".