What is the psychological basis of "survivor's guilt"? Context

I have just been watching a documentary about survivors of the Japanese earthquake and tsunami of March 2011.  Specifically the interviews with ordinary residents of the towns affected.

One thing came through time and again was the notion that was best stated by a friend of mine*- a volunteer firefighter on duty in one of the affected towns on the day of the tsunami:


  what gives me the right to survive, when so many others died?


Question

Obviously, this doesn't just occur in Japan, it seems to happen a lot, where people seem to feel guilty to have survived and feel a sense of responsibility for those who perished.  What is the psychological basis behind this?

Are there any studies that have addressed this?

Side notes

I lived in Japan for 4 years and have many friends from the affected area, this friend of mine was and is still inconsolable that he, in his own mind, could not save more people.
1. Psychological basis of survivor guilt

Psychosocial and evolutionary perspective on survivor guilt

Survivor guilt may be a psychological response that is associated with depression. Loss of a beloved one, which constitutes a psychosocial attachment, can precipitate a proneness towards experiencing survivor guilt. In clinical samples, the clinically depressed tend to suffer from pathogenic cognitions in which they view themselves as harmful to others are an effect of feeling guilty from surviving a beloved one's death (O'Connor et al., 2002). In that regard, we can hypothesise that survivor guilt is probably a self-protective mechanism involving self-denunciation to combat guilt about surviving a beloved one's death.


  Tendency toward self-reproach which death invariably leaves among the
  survivors (Freud, 1987, cited in Ernest Jones, 1960)


Survivor guilt could have evolutionary roots as well: survivor guilt may be a product of evolutionary pressures with living in small groups as a means to promote social organisation (O'Connor et al., 2002). The loss of an individual within these close socially-knit arrangements creates dysfunction and survivor guilt is an evolutionary means to understanding the changes experienced.

Existential crises, anxiety and ambivalence

Drawing from logotherapy, survivor guilt can be understood further from an existential point of view by referring to existential dynamics (Tate et al., 2012):


  Mental health is based on a certain amount of tension [or existential
  dynamics], the tension between what one has already achieved and what
  one still ought to accomplish, or the gap between what one is and what
  one should become. (p. 104)


Survivor guilt may be the tension created between an individual's past experiences and future possibilities. Past experiences such as traumatic events create tension with an individual understanding his or her existence compared to future potentialities. A person narrowly escaping death may physically survive the traumatic experience but in the present moment, they experience excessive amounts of worry about why they are here and what the future holds. This cognitive dichotomy of being shameful about the past and fearful of the future can lead to survivor guilt.

2. Studies on the psychological basis of survivor guilt

Post-traumatic stress disorder (PTSD), cognitive distortions and survivor guilt

Jones and Okulate (2006) conducted a study on the relationship between PTSD and survivor guilt by administering a questionnaire to 1,131 patients from the 68 Nigerian Army Reference Hospital, Lagos, Nigeria. Of these, 194 (22.09%) met the criteria for current 
PTSD. Survivor guilt was found in 336 responders (38.26%). The following explanation is given by the authors:


  The 
  reason for the very high rate of survivor guilt may be related 
  to the intra-group identification and cohesiveness that usually 
  develops in combat-effective military units after several years 
  of training together. Unfortunately, loss of men resulting from 
  death or injury in battle is inevitable. For those who survive, 
  witnessing the death of comrades is additional psychosocial 
  stressor to the combat situation itself, and the survivor guilt 
  that may result is understandably very distressing.


Survivor guilt and chronic illness

Vamos (1997) provides cases on patients and their experiences of survivor guilt in the face of chronic illness and witnessing other people's illnesses:


  Miss A had visited her frequently and  had repeatedly had the
  experience of trying to bright-  en her friend by accounts of shopping
  expeditions or  other excursions, only to feel profoundly guilt-ridden
  that she could still be enjoying herself when her  friend’s life was
  so limited. Since the death, she had  been unable to weep but had
  found herself compelled  to clean both the house and herself
  repeatedly, and  had often wondered whether she should take a  ‘break’
  from dialysis


References


O’Connor, L.E., Berry, J.W., Weiss, J. &amp; Gilbert, P. (2002). Guilt, fear, submission, and empathy in depression. Journal of Affective Disorders, 71(1), 19-27
Tate, K.A., Williams, C. &amp; Harden, D. (2012). Finding purpose in pain: Using logotherapy as a method for addressing survivor guilt in first-generation college students. Journal of College Counselling, 2012, 16(1), 79-92
Okulate, G.T. &amp; Jones, O.B.E. (2006). Post-traumatic stress disorder, survivor guilt and substance use – a study of hospitalised Nigerian army veterans. South African Medical Journal, 96(2), 144-146
Vamos, M. (1997). Survivor guilt and chronic illness. Australian and New Zealand Journal of Psychiatry 1997, 31, 592-596