There seems to be no default. When you want to enable the LVD interrupt you need to provide a voltage level. See "System Reference Guide" (from Creator Help)
Just from device perspective, this voltage threshold level is defined in LVD_SEL=PWR_VMON_CONFIG[4:1].
And the default value is LVD_SEL=PWR_VMON_CONFIG[4:1]=0. That mean 1.7500V is set.
Please check PSoC 4000 register TRM section 13.1.5 PWR_VMON_CONFIG.