Improve my graph in matlab

Hi, I have drawn this graph but i want to improve it. It is rays that goes from one point to get reflected and come back to a point in the upper line . how to put names on the points in the upper line . I want to put 'Earthquake' on the first point and receiver 1 on the second one ,receiver 2 on the 3 one, receiver 4 and receiver 5 on the 5 point.

How to give a different color to every line that goes down and get reflected?

matlab file

x=[0 20];
y=[0 0];
plot(x,y)
hold on;
axis off;
y1=[-5 -5];
plot(x,y1)
hold on;
x2=[ 0 2.5 5 0 5 10 0 7.5 15 0 10 20 ];
y2=[ 0 -5 0 0 -5 0 0 -5 0 0 -5 0];
plot(x2,y2)
title('EX4,SEISMIC MODEL, LAYER OVER A HALFSPACE')

Answer 1

[Walter Roberson]

I suggest you look at annotation() -- but sometimes just text() is good enough.