How does Shelly use the structural technique of the frame story in Frankenstein?

The  technique used by Shelly is referred to as EMBEDDED NARRATIVE

Explanation: referred

Embedded narrative refers to when the main story is told within a framing narrative. The composition of Frankenstein is more complex when compared to other novels.  

Shelly starts by making use of a framing narrative in frankenstein( Walton's letters to his sister), then proceeded to the main narrative which is ( victor's story). Still within that is how He  learns from the family of Delacy and the monsters story of survival.

Shelley is able to guide the readers towards the central ideas of the novel which might have been dismissed as beyond relief if she had introduced suddenly by the use of such complex narrative.

In other high point the themes of the novel from different viewpoints, Mary Shelly employ the three varied narrative technique.