Frequent UDP TCP Flooding

We are recently facing frequent DDOS attacks on our shared and reseller hosting servers located in ASIA and US. Types of attacks we are receiving is shared below:- [removed - please attach images directly to the thread] All these servers are with Linux CenTOS and cPanel/WHM installed on it. We have a limited access to the network as these servers are procured from DC itself. My Questions are:- 1. Is it the content/websites we are hosting causing the issue? 2. Are there any tools we can use to scan such type of vulnerable websites or content? 3. What else can be done to secure from such kind of attacks? 4. How to determine the source? Any help would be highly appreciated.