Tall concrete walls can indeed collapse in an earthquake. The ground shaking can exert excessive forces on the walls, and if they lack adequate reinforcement or are not built to seismic standards, they may give way.
One way is to check on popular fanfiction websites. Look for ones with high ratings and a lot of reviews. For example, Archive of Our Own (AO3) has a large collection of AOT fanfictions. You can search for the most popular ones there.
Another difference lies in the overall mood. Canon AOT has a rather dark, gritty, and often hopeless mood due to the constant threat of Titans. However, a friendly Titan fanfic would likely have a more positive, hopeful mood. It might explore themes of redemption for the Titans, or how their existence could be beneficial to the world of AOT. This is a complete departure from the doom - and - gloom feeling that often pervades the official AOT story.
It's fairly common. Fans often look for more content related to their favorite shows. Since 'Attack on Titan' has a large and passionate fan base, there are a lot of fanfics available. 'Aot' fans might watch (read) these fanfics to explore different scenarios that the official story didn't cover. For example, they might want to see how a certain character would react in a different situation or what would happen if a major plot event had a different outcome.
To find the best AoT fanfiction, consider the length of the story as well. Sometimes a longer fanfic can develop more complex plots and characters. But shorter ones can also be great if they're really well - written. Check the tags on the fanfics too. If it has tags that match your interests, like 'Eren x Mikasa' or 'Titan mystery', it might be more likely to be a good read for you. And don't be afraid to sample a few different ones. You'll soon get a sense of what makes a great AoT fanfiction by reading a variety of them.