hondana wa kabe ni koteishite atte, jishin no toki mo taorenikui.

The bookshelf is fixed to the wall, so it’s hard for it to fall over during an earthquake.

Breakdown of hondana wa kabe ni koteishite atte, jishin no toki mo taorenikui.

• は: topic particle
• の: possessive case particle
• とき: when
• も: even

Questions & Answers about hondana wa kabe ni koteishite atte, jishin no toki mo taorenikui.

What is the function of は after 本棚? Why not が?

は marks 本棚 (bookshelf) as the topic of the sentence: “As for the bookshelf, …”.

So the structure is:

• 本棚は = As for the bookshelf,
• (it) is fixed to the wall, and it is hard to fall over during an earthquake.

You could grammatically say 本棚が壁に固定してあって…, but that would sound more like you’re newly presenting the bookshelf as information (“the bookshelf is the thing that is fixed to the wall”).

In context, we usually already know we’re talking about “the bookshelf,” so は is natural to set it as the topic and then describe its condition.

What does 壁に固定してあって mean exactly? How does this grammar work?

Literally:

• 壁に = to the wall / on the wall (particle に = target/location)
• 固定して = fixing / having fixed (て-form of 固定する, “to fix, secure, fasten”)
• あって = て-form of ある

The pattern ～てある describes:

a resulting state that exists because someone intentionally did something.

So 壁に固定してある ≈ “(it) has been fixed to the wall and is (now) in that fixed state.”

In the sentence, the verb is in て-form with あって and then linked with 、 to the next clause:

• 壁に固定してあって、地震のときも倒れにくい。
  = “It is (in the state of) being fixed to the wall, and (therefore) it’s hard to fall over even in an earthquake.”

What’s the difference between 固定してある and 固定している?