Peritraumatic reactions such as fear, psychic and somatoform dissociation, tonic immobility, data-driven processing, and mental defeat are important in the etiology of posttraumatic stress disorder (PTSD). However current measures of such reactions overlap conceptually and do not clearly identify distinct peritraumatic processes. It is not known which processes are uniquely associated with PTSD. We investigated the factor structure of six standard peritraumatic measures and their relationship with the four DSM-5 PTSD symptom clusters. Measures were administered to 308 earthquake survivors with high levels of exposure to traumatic events. Items comprising the six measures were investigated using exploratory structural equation modeling, which identified five peritraumatic response factors. Items from most measures loaded on multiple factors. The factors labeled Mental Defeat and Somatoform Dissociation significantly predicted all PTSD symptom clusters. The factor labeled Cognitive Overload significantly predicted Intrusions, Avoidance, and Alterations in Arousal and Reactivity. The factor labeled Immobility significantly predicted Intrusions and Avoidance while Distress significantly predicted Negative Alterations in Cognition and Mood and Alterations in Arousal and Reactivity. Due to the key role such reactions play in the development of PTSD, the findings are likely to benefit the study of etiological mechanisms, the prediction of those at greatest risk, and the design of preventative interventions