Achievements and prospects of global broadband seismographic networks after 30 years of continuous geophysical observations by Ringler, AT, Anthony, RE, Aster, RC, Ammon, CJ, Arrowsmith, S, Benz, H, Ebeling, C, Frassetto, A, Kim, W-Y, Koelemeijer, P, Lekic, V, Lau, H, Montagner, J-P, Richards, PG, Schaff, DP, Vallée, M, Yeck, W