"Consider a scenario where you are tasked with designing a long$-$span bridge over a river in a seismically active region. Discuss in detail the key factors you would need to consider in the design process to ensure the structural integrity and resilience of the bridge against seismic events. Outline the structural elements, materials, and design principles you would employ to mitigate the effects of seismic forces while maintaining the functionality and safety of the bridge. Additionally, elaborate on the importance of geotechnical investigations, dynamic analysis, and construction techniques in achieving a robust and earthquake$-$resistant bridge design. Finally, discuss any innovative approaches or emerging technologies that could potentially enhance the seismic performance of long$-$span bridges in such environments."