Korean brokerages are rapidly expanding their capital bases on the back of a robust stock market rally, though the rapid scale-up is fueling concerns over declining profitability and greater exposure to volatile markets, industry officials said Thursday. Korea Investment & Securities saw its equity capital jump 18.2 percent to 13.19 trillion won ($9.46 billion) in June, up from 11.16 trillion won last December, driven by strong earnings and proactive capital raises to fund new ventures. Medium-sized firms also posted steep growth. KB Securities saw its equity capital jump 19.2 percent from 6.69 trillion won to 7.98 trillion won, recording the highest growth rate among the top eight brokerages. Peers including Kiwoom, Meritz, Hana and Samsung also posted solid gains. The capital expansion comes as brokerages benefit from a broader rally in the benchmark KOSPI and the diversification of revenue streams beyond retail stock trading. “Brokerage earnings have recently improved on the back of simultaneous growth in investment banking, wealth management and trading services,” Ahn Young-joon,