In interviews with the workers who changed jobs, Granovetter learned that the contacts who helped them land the job were most often an old friend, a former co-worker, or former employee. In addition, that contract was liekly to be someone with whom that worker had maintained sporadic contact over the years. Granovetter called these.

Granovetter call these WEAK TIES

Explanation:

Weak tie theory is the proposition that acquaintances are likely to be more influential than close friends, particularly in social networks. Weak ties that connect social networks are sometimes called bridges. Absent ties are connections that are expected to exist but do not. According to a study, the more weak ties a person has the happier they feel. Maintaining this network of acquaintances also contributes to one's sense of belonging to a community.

the factors that the economies of the muslim empires prosper were:

1- land trade routes-located between three continents  

2- sea trade routes

trade contributed to the spread of muslim empires, and with that islamic culture led to a growing feeling of internationalism resulted in the transfer of technology, science, and other cultural forms.

earthquake fault lines