Today: Facebook's mobile-advertising revenues help company beat Wall Street expectations, push stock up more than 20 percent. Also: Google (GOOG) introduces new television offering and Nexus tablet; tech stocks bolstered by post-earnings bounces by Apple (AAPL), Electronic Arts (ERTS) and VMware.

The Lead: Facebook's mobile growth, earnings demolish expectations, stock roars

Facebook's mobile revenues shot higher in the second quarter of 2013, helping the Menlo Park social network boost profits and revenues beyond analysts' expectations and spurring investors on an after-hours buying spree that pushed share prices to some of their highest levels since the company's initial public offering.

Facebook reported profits of 13 cents a share on revenues of $1.81 billion for the April-June period, easily defeating Wall Street expectations of 9 cents a share on revenues of $1.62 billion, according to Thomson Reuters research. In the same quarter a year ago, which included the company's IPO, Facebook lost 8 cents a share on revenues of $1.18 billion.

Mobile advertising received most of the credit, as Facebook reported that 41 percent of its advertising revenue came from mobile usage, a big jump from the first quarter, when the company reported that 30 percent of its revenue derived from mobile ads.

The need for such revenues was underlined by the company's data on mobile users -- 469 million Facebook users accessed the platform daily on mobile devices and 819 million used the mobile platform monthly. Total active users by those standard was 699 million and 1.15 billion, as mobile usage continued to account for more than half of Facebook's total.

"The work we've done to make mobile the best Facebook experience is showing good results and provides us with a solid foundation for the future," co-founder and CEO Mark Zuckerberg said in Wednesday's news release.

Facebook's stock exploded higher after the results were released. Facebook closed Wednesday's regular session with a 1.5 percent advance to $26.51, but shares sold for as much as $31.98 in the first hour and a half of late trading, an increase of more than 20 percent that came close to the 52-week high of $32.51.

Analysts seemed as excited as investors, with Bloomberg Industries analyst Paul Sweeney dubbing it "the blowout quarter that Facebook bulls have been waiting for." Sterne Agee analyst Arvind Bhatia pointed out the rise in mobile advertising did not seem to dissuade users from accessing the service.

"The company is successfully making the transition to mobile and new ad formats are working really well. Facebook's ad exchange works really well. Engagement is fairly strong still, so it doesn't sound like anyone is really being turned off by these extra ads," Bhatia told Reuters.

In other Silicon Valley earnings reports, Palo Alto's Varian Medical Systems boosted profits and revenues, earning $1.03 a share on revenues of $726 million; San Jose's LSI reported profits of 4 cents a share on revenues of $590 million while initiating its first cash dividend; San Jose chip-equipment company Cadence earned 3 cents a share on revenues of $362 million, with profits falling but revenues rising; Sunnyvale's Infinera continued a pattern of growing revenues and slimming losses, posting a loss of 9 cents a share on revenues of $138.4 million; Sunnyvale chip firm AppliedMicro made a huge swing to profits on one-time revenues from selling part of the business, giving it profits of 15 cents a share on revenues of $54.1 million; and Fremont's Exar earned 2 cents a share on revenues of $32.6 million.

Google shows off Chromecast TV offering and refreshed Nexus 7 tablet lineup

Google gave tech observers what they expected in its event Wednesday, introducing a refreshed lineup of Nexus 7 tablets with incremental improvements in features such as screen resolution and graphics capability. However, the Mountain View search giant threw in an unexpected bonus, introducing Chromecast, a small dongle that uses Chrome browser technology to broadcast streaming Internet video to a user's television set.

The Chromecast connects to a home wireless network and can be controlled with a tablet, smartphone or personal computer; the device can then be commanded to stream information from the Web, such as from YouTube or Netflix (NFLX), and can then take over while allowing the device to function separately. In the end, the device performs a similar function to other dongles and offerings, such as a Roku player or Apple TV, but at a lower cost: Google is selling the Chromecast, which doesn't require further subscription fees, for $35, and including three months of free Netflix service.

The aim of the Chromecast is similar to the Nexus Q, which Google announced a year ago but never released, and follows the Google TV service it bundled with certain television sets. Forrester analyst Sarah Rotman Epps called the Chromecast a "smaller, more elegant approach" than Google's previous efforts, and the device is already on sale in the Google Play store and will soon be offered by Amazon and Best Buy, avoiding the Nexus Q's fate.

The new Nexus 7 line of tablets from Google were said to have the highest-resolution screens available for 7-inch tablets, and will ship with the newest version of Android Jelly Bean. The popular devices will start at $229, $100 lower than the iPad Mini, but still more expensive than Amazon's Kindle line of tablets.

Google stock fell 0.1 percent to $902.90 Wednesday.

SV150 market report: Apple, EA and VMware shoot higher after earnings reports

While major stock indexes struggled Wednesday, Silicon Valley stocks received a huge boost from Apple and other tech companies that released earnings Tuesday afternoon, sending the SV150 index up 1.4 percent.

Apple gained 5.1 percent to $440.51 after beating Wall Street's expectations for iPhone sales, though concerns about the Cupertino company's ability to grow in the Chinese market held may have it back from more gains. VMware and Electronic Arts performed even better than Apple on a percentage basis Wednesday, with the Palo Alto software company experiencing the biggest leap. After reporting strong gains in profits and revenues, VMware had its best day on Wall Street in more than four years, gaining 16.7 percent to $83.20. Redwood City video game developer EA almost eclipsed its highest price in the past five years after its earnings report, gaining 6.7 percent to $25.51. San Jose web video company Harmonic joined the party, establishing a new 52-week high and closing with a 10.6 percent gain at $7.70 after its earnings report.

On the negative side Wednesday was Polycom, the San Jose videoconferencing company that forced out its CEO after discovering irregularities in his expenses; shares declined 15.1 percent to $9.49. Juniper Networks, which also announced its CEO's departure Wednesday, gained 1.5 percent to $21.66, as the departure was balanced by a strong earnings report.

Up: VMware, EA, Apple, Workday, Yahoo (YHOO), LinkedIn, Juniper, Hewlett-Packard (HPQ), Facebook, Gilead, Oracle (ORCL), eBay (EBAY), NetApp, Symantec, Intel (INTC), Zynga, Cisco

Down: Netflix, SunPower (SPWRA), SolarCity, Salesforce, Intuit (INTU), Applied Materials, Tesla, AMD, Adobe

The SV150 index of Silicon Valley's largest tech companies: Up 17.04, or 1.36 percent, to 1,267.71

The tech-heavy Nasdaq composite index: Up 0.33, or 0.01 percent, to 3,579.6

The blue chip Dow Jones industrial average: Down 25.5, or 0.16 percent, to 15,542.24

And the widely watched Standard & Poor's 500 index: Down 6.45, or 0.38 percent, to 1,685.94

Check in weekday afternoons for the 60-Second Business Break, a summary of news from Mercury News staff writers, The Associated Press, Bloomberg News and other wire services. Contact Jeremy C. Owens at 408-920-5876; follow him at Twitter.com/mercbizbreak.