Question Two questions

[zuotengdazuo]

Hi. I have two simple questions here. Does the 出現していた indicate that they habitually appeared in the past? Can we use 出現した here? Or because of the existence of 以前 we have to use ていた here?
And does the underlined もの refer to 空間震被害?
Thank you.

 

[Toritoribe]

Does the 出現していた indicate that they habitually appeared in the past? Can we use 出現した here? Or because of the existence of 以前 we have to use ていた here?

Yes, yes and no.

does the underlined もの refer to 空間震被害?

That's a typo of ものの.