Reallocing an array in C

I'm trying to create a function that would append two vectors together, but I end up getting a segfault when trying to reallocate more memory to the first vector so the second one would fit. Here's the code

void vectorAppend(double** v1, size_t* s1, double const* v2, size_t s2){
  assert(v1 && v2 && *s1 > 0 && s2 > 0);
  (*v1) = realloc((*v1), (*s1 + s2)*sizeof(double));
  for (size_t i = 0; i < s2; i++){
    *v1[*s1+i]=v2[i];
  }
  *s1+=s2;
}

And this is how I call it from main

double *v1 = vectorConstruct(3, 2);
double *v2 = vectorConstruct(3, 0);
unsigned int s = 3;
vectorAppend(&v1, &s, v2, 3);

vectorConstruct returns a pointer to a vector that is initialized to the second argument.

double* vectorConstruct(size_t s, double val){
  assert(s>0);
  double *ret = malloc(s*sizeof(double));
  for(size_t i = 0; i < s;i++){
    ret[i]=val;
  }
  return ret;
}

I can't seem to find the problem here so any answers are appreciated.