On first inspection there appears to be little similarity between the two films, you notice all the obvious aspects, such as the role of photographs (they are deeply relayed on in both films as evidence) and how both films open up with a shot of a photograph (that's where the plot begins) but you only begin to realise all the similarities when you take a closer look and consider all the noir attributes. .
Like the original noirs both films are based on Investigation, both of the main characters are detectives and work alone (In both cases they have lost their jobs as police men due to a loss). The films are very close to their origins (1940's and 60's noirs), they include male characters who are the protagonists, which have very similar characteristics as original noir films (they both have conventional characters). In each characters case, he is caught between his conscience and those desires, which violate normal society and morals. In noir films male characters are separated into two categories, for both films they have opted for the "Seeker Hero" who is stronger than the "Victim hero" but is still influenced/ controlled to an extent by the female of the piece. .
Natalie in memento has very similar characteristics to Mrs Morey in Chinatown. Both character are "Spider women" (who capture men in their webs) and are central to the intrigue of the film. Both women are alike the original "femme fatales" often seen in original noirs, both are not placed safely in their roles and are defined by their sexuality. Both are presented as desirable but dangerous to men and function as an obstacle to the male quest (Natalie is an obstacle because of her manipulation to get Lenny to do things for her and Mrs Morey as Jakes conscience to do the right thing for her and try to save her, instead of just going to the police. Also she withheld information from him).
In both films the main characters are manipulated to some extent (Lenny by Natalie and Teddy, Jake by Mrs Morey (real and fake) and Mrs Morey by her Father).