San Francisco is sandwiched between two major earthquake faults. You can’t see them. But that doesn’t mean they’re not there.

Some fault lines lie deep beneath the earth. But some are man-made; earlier this month, one of the latter variety ruptured in Dolores Park. A confrontation near the footbridge over the J-Church tracks at 19th St. culminated in a brazen, daylight shooting. Three people were sent to San Francisco General, and scores of men and women lolling in the grass at San Francisco’s premier lolling site dropped their beers and ran like hell.

San Francisco, like every city, has built over its past. But, at times, elements of the past come back into full view. And while the spectacular influx of cash into this city — and, specifically, the Mission — has transformed Dolores Park from a scruffy, lawless realm into a verdant DIY biergarten and expensive playground where tattooed, bearded men push Zelda and Brooklyn on the swings, that money hasn’t ameliorated the conditions that once made desperation and crime synonymous with this spot.

The very bridge where gunfire broke out on Aug. 4 has, for generations, been known as an outpost for gangs and drugs. Per multiple San Francisco Police Department sources, this attack had everything to do with the former — but little, if anything, to do with the latter.

Dolores Park, numerous SFPD gang and narcotics officers say, is the territory of the “Dolores Park Locals,” which they characterize as a Sureño clique. Over the past year, police say they have documented increased gang graffiti in the park; violence has flared up and tensions have been simmering (cops summed up other recent incidents, such as a May mob attack, as cases in which “outsiders” wandered into locals’ territory).

“It’s, like, the ebb and flow, man,” said one veteran Mission cop. “There’s a lot, and then there’s not. Or maybe it’s the same amount of guys and they’ve just got somebody pushing a hard line up there.”

While much of the purported graffiti has been of the MS-13 variety, that’s not who our sources thought was responsible for this month’s violence. Who shot whom in an ongoing investigation isn’t something police are in the habit of talking too much about, but one source did state he believes the shooting was the work of “young Norteños trying to make a name for themselves.” He adds, reassuringly, “I haven’t heard it’s a war yet. I’m not hearing names and stuff yet.”

Cops who work the park candidly say that, beyond serving as “a visual deterrent,” they don’t have any advanced notions of how to quell the next daylight shooting. If our sources are correct, the Aug. 4 incident — along with others preceding it — was likely not explicitly tied to drugs. In the past, however, that’s the hammer the police would have used to crack down on park mayhem — regardless of the cause.

Will this be happening in Dolores Park now? Laughter. Maniacal laughter. “Are you really going to go up and do a buy-bust in Dolores Park — for weed? In 2017?” asks a veteran Mission cop. More laughter. “Weed is pretty much legal now.” (And, next year, you can do away with the “pretty much.”)

Responding to violent crime (and what appears to be directed gang violence) by engaging in a shotgun approach against pot dealers was the cops’ go-to strategy for decades. But the utter ridiculousness of even considering such a move in present-day Dolores Park — which could sweep up vast numbers of minor criminals and non-criminals and bearded men pushing Zelda and Brooklyn on the swings — reveals how problematic it always was.

Cracking the underlying causes for gang violence in the Mission, it turns out, is a lot harder than using weed busts to ensnare gang members. “Our whole industry has not figured out the crime problem yet,” says a member of the police department’s gang task force. “I don’t expect it to anytime soon.” Instead, he’s hoping for “a little luck” and, maybe, “finding some sort of video.”

Doing away with buy-busts, veteran cops complain, is part of a larger trend away from proactive policing. A rich, citywide vein of snitches has been lost, they bemoan. “You wanna know what’s going on in Dolores Park?” postulates a longtime narc. “Go to 19th and San Carlos and jam those guys.” The gang member popped in a buy-bust in the Tenderloin might be the one to roll on his associates in the Mission. And, even without buy-busts, the narc continues, there used to be more of an emphasis on everyday, minor shakedowns — “humbugging ‘em” — in exchange for information. “You don’t even have to arrest them: ‘I’m gonna let you go, but next time, I need something,’” he explains. “It’s like breaking the ice with a woman.” The cops, he sighs, used to be players in this game. Now they’re just scorekeepers. And nobody is getting out ahead of the gangs.

As such, the cops’ 2017 Dolores Park strategy will “be like Groundhog Day. You know exactly what they’ll do,” says another longtime narc. “They’ll have a big enforcement plan. You’ll see a ramped-up effort for a month, two months. And then it’s back to business. You can’t sustain it. Cops, at this point, are like firefighters. There’s a big fire at Dolores Park? Go put it out. Monitor it a while. And then, in the future, you and I will be having this same conversation.”

Does it make sense for cops to be posted in the park like scarecrows, pushing crime and trouble to the less-beautiful parts of town? Officers rattle off places where shootings and crime are inevitable — Third and Palou, the Tenderloin — but there is not a plan afoot to flood these areas, which have not yet received multimillion-dollar facelifts and are not ideal lolling spots. Why should people in Bayview and the Tenderloin be forced to accept misery and crime as inevitable? Is there a double-standard here?

“Of course there is! You need to ask such a question?” scolds a retired Mission cop. But then he points the finger back at us. When gunfire erupts in places where we expect — and accept — gunfire, it’s no big deal. “But if someone with a job and a mortgage and a station wagon gets killed, then it’s a big story.”

Cops ambling around Dolores Park will likely reduce incidents, just as an empty CHP car with flashing lights will induce drivers to slow around a curve. But it doesn’t even begin to address the root causes. It’s not designed to.

And that’s the problem with reactive policing — and reactive policies and reactive politics and, yes, reactive reporting. You’re only reacting to what you can see. But there are so many things you can’t see, and won’t see. Until it’s too late, and that’s all you can see. This city is, literally, built on that.

On Aug. 21, District 8 Supervisor Jeff Sheehy will host a community meeting to “discuss public safety with SFPD and other City agencies operating in the park” at 6 p.m., 455 Dolores St.